Getting a GC would be the best way to do this job.

Designer Drains - TY for your response. Had contractor in mind but wanted others' input before hiring.

https://www.ceramictilefoundation.org/homeowners-guide-to-hiring-qualified-tile-installer

https://nkba.org/info/why-hire-a-designer

https://www.nahb.org/en/learn/designations/certified-aging-in-place-specialist.aspx

TY Sophie.

I have looked at a lot of shower designs for aging in place and in my searching I don't remember seeing a TUB with a built-in bench. The exceptions are the walk-in tubs with the doors. There are a lot of benches that can be mounted onto the walls of a tub, though. Here is a teak one. See how the right side clamps onto the bathtub wall?

Considering the molded technology that tub makers use these days, a
bench would be likely to be molded right into the design, meaning there
would be no "tub" going under it. The best case scenario would be a groove at the top of the tub to hold a removable bench. But either the bench would have to be higher than the tub spout, or on the other end from the spout, which would leave the bather with no long wall to lean on in most tubs.

The walk-in tub is the only real common tub with a built-in bench. You can use the search box at the top of any Houzz page to search for "walk-in bath tub" and chose "shop," and get nine pages of them to see.

The holder for the handheld shower head is an easy thing. It can be a safety handrail at the same time, if you want it to be vertical. How much do you want to spend on it? They start around $105 for this one and go up to $800 or more for ones that look fancy and are brass with chrome plating or other finishes.

With this one, you can locate this bar down near your bench and be able to use the bar to help you rise, to hold the water as you wash while sitting down there, then put the hand held shower head in the holder at the traditional shower position for when you want to shower standing up. The holder on the bar will slide up and down the bar so you can position it anywhere.

TY Nancy for this great info, especially re the showerhead holder. Will likely instead buy a portable transfer bench, which sits half in the tub, half outside of it. But the holder you suggested should definitely work.

You are welcome. Be careful with those benches. Getting the shower curtain around them to keep in the water is a pain! You may want to just cut a curtain shorter for the area going over the bench.