I'm 62 and thank the Good Lord I don't suffer from anything but the usual old-age stuff......
I know everyone just can't do it but I bought a 2 post lift..it really makes the low down stuff a LOT easier...for me getting down on the floor is easy...getting up is what's hard...hahaha
A good creeper is a must...but I also bought a "Topside" creeper....basically just a ladder with a platform that goes over the top....a must for lifted vehicles....really take the strain off the legs
Other than that....air tools can really make life easier....even the electric impact tools work well....
so glad to hear of women who work on their own trucks and I'm sorry that you must endure the pain of RA....
best of luck with all you do..>!