Here's a handy map of Wilderness areas in Colorado:
At least it can give you ideas to research.
When are you doing the hike? And what do you mean by "southern" Colorado? The southern half of the state, or the southern third, etc.?
It has been a really disappointing snow year here- the snow pack is only 60% of average- but there was still an annoying amount of snow at the higher elevations in the San Juans when I drove through in the first week of April. At anything other that truly alpine elevations, though, almost everything is passable by now. maybe someone else can give you more recent conditions.
That said, if you're doing this a couple of months from now the San Juan and Weminuche wildernesses are on MY life list. Both have many trails that can be hitched together into loops of varying length. Just buy the appropriate Trails Illustrated map and make a route. there's even a hot springs just a day-hike in to the Weminuche.
The Sangre de Cristos don't have as many loop possibilities, but there are a few. I remember researching them a while ago but never got to do the hike. You can also cross the mountains into Great Sand Dunes National Park if you like, fitting any of the several passes together- use one going and another coming back. That'd be epic, but possibly longer than you want.
I'll try to remember to peek at my maps when I get home and see if I can be more specific.