Buffalo Peaks Wilderness.
There is a valley hike linking together Rich Creek Trail, Tumble Creek Trail, and Salt Creek Trail. Complete loop travels all the way around the Buffalo Peaks and is 20+miles. Close to Denver, Fishing in various Beaver Ponds, easy hiking without significant elevation gain. Relatively high altitude hiking in the 10,000-11,500 zone. To get there you take Highway 285 South of Fairplay. Turn West on CR 22, follow to Rich Creek Trailhead.
You start at the Rich Creek TH and proceed west along the Rich Creek Trail. After about 6 miles you will come to the convergence with the Tumble Creek Trail. You can proceed south and eventually back East as you circle West and East Buffalo peaks which are 13k ft peaks that the wilderness is named after. I haven't been on this southern segment of that trail but the USGS map shows the trail distinctly. You eventually catch the Salt Creek Trail which takes you back to the North to rejoin the Tumble Creek trail and eventually back to the Rich Creek TH. Personally, I think this is the very best option considering your companion that is recovering from Back issues. The trail is very well defined and the elevation gains are modest and hiking very scenic.