I'd recommend two different routes, whichever you and your pocketbook prefer.
If you hike with poles (and you should, especially with the knee issue), then look at the pyramids. I have type of arthritis that severely limits all of my flexibility and the MLD duomid is an absolute dream come true. Soooo easy to set up, the entryway is huge, and I can get in and out of the solo inner net without any troubles at all. The entryway is something like 4.5' tall. Awesome.
If a pyramid is not your style, then do look at tarptent. Dena is very correct about the side entry...don't even bother with a front loader. I have the stratospire 1 as well and it, too is an amazing tent. It's heavier, though... You could go lighter with the notch, but it's smaller; it just depends on how much space you want.
My cuben fiber duomid and inner net weighs all of 22 oz, including all the guy lines and whatnot. So super light, sets up easy, packs small...I just can't say enough good things about it.