I think you should plan for grab bars for the safest assistance in getting out of a bathtub. Some of them are very nice. I bought some that match other fixtures even though I am not installing them right now.

People choose a drop in tub because it's easier to install than an undermount which must have a carefully fabricated reveal, and also some people do not like undermount because of the caulk joint under the edge.

My bathtub has integrated grab bars. I would use the side of the tub or tub wall unless I was so decrepit I couldn't straighten from bending over without help. Then I would install more grab bars. But honestly, your well used gym membership is a better investment in aging in place at this point.

The integrated grab bars are useful because the tub is so deep that I just about float in it. :) They make sliding down and up surprisingly easier. And unlike the elbow shelves in my Kohlers, they don't make cleaning a pain.

For aging in place, we just installed an undermount, not too deep, with a really elegant grab bar. I want to be able to sit on the tub deck and swivel around into the tub if I have to, not maneuver around a thick lip. I really hated the drop in we replaced because it was so thick. (Even now, I sometimes like to soak my feet in the tub before doing a pedicure, and a lip is uncomfortable.). We offset the shallow tub with one of MTI’s elevated slotted overflows.