We have the same issue-- only 1 bathroom upstairs, no way to add one without putting an addition on the house. I feel similarly to previous posters--i do not want my bedroom in the basement, nor did I want to be so far away from my kids at night.
Our solution was to finish the basement, with egress window and full bath. We use the space as a family room/ guest room. The kids loved the new bathroom and wanted to use it. DH is an early riser, so he showers down there too. So I pretty much had the upstairs bathroom to myself.

Kids are in college now, DH (and kids when they're home) still uses the basement bath almost exclusively.