Another possible solution.
If the bras don't work, or are too tricky to get on or off, etc etc, here is another suggestion.
Get hold of a long (ie, not square) scarf made in a soft material - not fleecy, but cottony ideally (not silky, though that might work)and use that to wind around your wife's ribcage, underneath her breasts. The soft material of the scarf will prevent the dreaded 'feminine chafing' (!), but because the scarf is only tied around the ribcage, it's loads easier to get on and off, or lift to apply creams etc etc.
It's effectively a very soft bandage, that separates the 'weight' of the breast from the ribcage. It also serves to 'lift' the breast a little, so makes the 'drag' factor less uncomfortable! (I have NEVER known why girl complain of being flat as a pancake - LOADS MORE COMFY DEARIE!!!!!)(OK, when young, I can see the disadvantage re blokes etc etc!!!!!)
For cheap scarves, your best bet is charity shops - there's always a good choice there, and are cheap enough for you to try out several lengths (they do need to be about four foot, I would think, ideally, though shorter can work, depends on the size of your wife's ribcage!), and you will want several re laundry (especially if they are getting greasy with sudocream etc etc)
Good luck with it all! What devoted hubby you are. She's a lucky lady, your wife!