I have mild COPD, and foot problems. I tried a treadmill, but it aggravated my foot issues. I decided to try an elliptical machine, but the size and cost ($400-600+ _used_) of them was off-putting.
I got really lucky... I was waiting to talk to the salesdroid at the local second-hand sporting gear shop when a guy brought in the smallest elliptical machine I've ever seen. It was brand new, never used. It's an "Eclipse 1100". I got it for $149. Retail is about $250+.

(Sorry, this model doesn't come with that model....;))
It does not fold, and it is heavy, but has rollers. It's a bit awkward to mount and dismount. It does have some bad reviews for breakdowns, but I've had no issues at all. It's compact and can be used for a legs-only workout that simulates a high-stepping walk, holding the stationary inner grips.
Dunno if this does you any good or not. Hope you wife has a speedy recovery.
Jim, "Mo' coffee!"