That is my current plan. I'm looking at a bunch of ryokan onsen in Hokkaido with private bathing rooms. The coed idea was more of a workaround than a fixed decision. I wanted to avoid getting pigeonholed but it looks like that's the best solution to the problem. I will be taking at least two day-trips to onsen by myself as well as going to a sento or two in Tokyo. Although if you guys keep it up with the great suggestions, I may have to add a third day!