I struggle with keeping my house too, and have really tried to identify the things that wear me out the most and ways to make things easier on myself. A housekeeper isn't an option for me either unfortunately!
For me, vacuuming was my nemesis- I'd haul the heavy beast from the closet, unwind the cord and get it plugged in, vacuum one area and I'd need to rest. Then I'd forget and do laundry or something instead of finishing, then chastise myself for forgetting while resting from the laundry. Next thing I know the vacuum has been sitting out for a week and is starting to get dusty, but I can't put it away because it was such a pain in the ass to get out I'll be damned if I won't finish.
Fast forward to the day I got a Dyson cordless vacuum... Hallelujah! It's super lightweight and powerful, no heavy cord to deal with, easy to grab for quick jobs and doesn't tire me out to do the whole house. This probably has made biggest difference for the cleanliness of my house.
For the bathtub, I got a Clorox toilet wand just for the tub - the pads have bleach and work great on the porcelain and the handle makes for less bending.