I now live in Sapporo. I would suggest that thinking about towns is not how you will locate the best backcountry skiing in Hokkaido. The best venues for the most part are not in towns. You will do better to target the ryokan (hot spring inns) that are at the ends of roads and at the foot of the goods. You would be surprised that there are not that many venue but that is because although Hokkaido has a lot of wilderness, it is not accessible in winter.
If I may suggest two places, they would be Tokachidake Onsen in the Tokachi Mountains of Daisetsuzan National Park and Rishiri Island, in the Japan Sea off the northern tip of Hokkaido.
First Tokachidake Onsen:
The Tokachi Mountains are a line of 7000 foot active volcanoes in the southwest corner of Daisetsuzan National Park. They are directly across the valley from Furano but are so different they warrant their own region in Hokkaido. The road going up out of the town of Kamifurano is about 18 km to a junction at the trailhead for Furanodake. There are about 4 or 5 ryokan in this area. My favorite is Hakuginso at Fukiage Onsen at the winter closer end of the road to the left of the junction. Hakuginso is owned by the town of Kamifurano and it does not serve food. There is a communal kitchen that you can use to prepare your own meals and there is a good supermarket down the hill in Kamifurano. This is my preferred accommodation for a number of reasons. It is very reasonable, 3250 yen per person per night. The sleeping is in dorm bunk beds or tatami rooms. The hot spring is the nicest one in all of Hokkaido. It's really special. You can only make reservations by phone and will need to find a Japanese speaker to help you. Nobody there speaks much English but they are very nice.
Hakuginso is at the foot of a wide variety of terrain. You are sleeping right at the trailhead so there is no commute from town. Out the back door you have Tokachidake and Maetokachidake, the active volcano that last erupted in 1988. It is due for another eruption as it tends to erupt on a thirty year interval. The lodge is full of information about the volcano and up to date information on the status of its activity. Also out the back door is Sandanyama, a nice peak with good skiing on several different aspects and some below tree line terrain that is friendly in the worst weather.
Back at the junction is a small parking area for Furanodake. You park and cross the road, then walk downhill about 200 meters to an obvious entry that drops you down to the creek, where an easy crossing puts you on a skin track that splits into two directions. One is up a valley to the right toward a crossing to gain Giant Ridge, which leads eventually to the summit of Furanodake. The left branch goes up a narrower, steeper ridge that quickly brings you to steep tree shots down to the valley that are easy to lap quickly. This side is clearly avalanche terrain so be prepared to bail when storm slab or wind slab conditions are present. Either route brings you to the summit of Furanodake, which has a number of very rad chutes, including one directly off the summit facing north. People tend to park in the road when the parking area is full and the police hate this and threaten to shut down access every year. So please, if you want to ski there and the lot is full, dig out parking in the snowbanks so you do not block the road at all. If this is not possible, continue up the hill to what I think is a better location for touring anyway.
If you go straight up past the junction (left if you are coming down from Hakuginso) you go up a steep road past a couple of hotels until you eventually reach the end of the road and a large parking area next to Ryounkaku, the highest onsen in Hokkaido. Right next to the inn, there is a steep drop of a couple hundred feet to a narrow creek crossing and a skin track that leads up into some complex terrain that holds excellent skiing on shorter but really high quality terrain in a large basin to the east of Furanodake. I really enjoy this area. It is all getting more discovered but there aren't any other venues quite like it. It's superb backcountry skiing. I don't recommend basing out of Kamifurano because the accommodations at the trailheads are so much better than anything you will find in town and you can relax and ski right out your door on a number of different options.
Second and the best place I know of on earth is Rishiri Island.
Rishiri Island is remote and stormy. The island consists of a single, deeply eroded, extinct volcano rising 1721 meters out of the sea. You can get there by airplane from Sapporo's urban airport, Okadama, or by ferry from the town of Wakkanai at the northern tip of Hokkaido. I like to use the ferry because it is less affected by bad weather than flying. It's a long way from anywhere but totally worth it. You can get to Wakkanai by car if you rent one or by bus or train. Trains are a pain in the ass to travel on with gear. I always take the bus. The ferry from Wakkanai to Oshidomari on Rishiri takes about an hour and 40 minutes.
On Rishiri you would have a hard time getting to the goods with only a car. The approaches can add 5-7 km of flat approach to your day, severely limiting what you can accomplish if you don't go with a guide who has snow machines and knows the mountain intimately. Fortunately, this is easy to arrange. Toshiya Watanabe is the local guide who grew up on Rishiri Island and has climbed Mount Rishiri more than 500 times. He speaks decent English and is a super great guy. He owns a ryokan in Oshidomari and has numerous associate guides working with him, a number of vans, and of course, sleds to get you to the goods quickly in the morning. His guiding fee is very reasonable and the client to guide ratio is always small. Given the fickle weather on Rishiri, the guides also will take you to the best terrain and snow considering the recent weather patterns. Storms hit Rishiri quickly from all directions so having these local guides will ensure you get the best of what this amazing island has to offer. The name of his lodge is Rera Mosir and you can contact him at https://www.explore-share.com/mountain- ... -watanabe/
Last week I spent four days with Toshi and his guides and in the worst winter in 70 years in Japan, I just had the two best ski days of my life. The food at Rera Mosir is fantastic and it the accommodation is clean and reasonably priced considering where you are and what you get. The rooms are either twin western beds or tatami mats and are less than $100 US per person per night including two excellent meals. You'll stop at a convenience store to buy your lunch on your way to the trailhead of the day in one of Toshi's vans. Guiding fees are 12,000 yen per person per day, or a little over $100 US. Sled use is usually about 2000 yen per person per day and is paid to the assistant guides in cash.
The weather on Rishiri is horrendous. It can be very windy and as I said, the snow can come from any direction. But there is always a protected valley somewhere among the ridges that radiate out 360 degrees around the summit. It is rare to get to the summit but even below an elevation of 1000 meters the skiing is out of this world,. 1500 to 1700 meter days are the norm as long as the weather isn't too bad. Yes, there is the risk that you will get shut down by weather some days, but if you go there for a 5 night, 4 day trip, the days the weather is not too bad will be amazing.
There are other places you can go, but these are the two venues I recommend. Hakuginso is very inexpensive and Rishiri is more costly but you get a value and experience for your money there that you will not find anywhere else that I know of. Here is a drone video of Rishiri with some clear weather. I am in it at a couple of moments (tele skier).