You don’t mention how much room you have for a shower. The tub could be an alcove 30x60 with a toilet beside it. Instead of guessing and throwing out useless ideas to you, you need to provide more information.

My house came with a one piece acrylic shower stall and we will soon be rid of the thing. It is so hard to clean. The floor is stained even though we don't walk around barefooted. There are two corner benches which turn pink from that bacteria that hangs out in showers. We've never even used the benches. I would advise you to avoid benches and multiple niches, places that mildew can collect.

We took the sliding doors off last fall in preparation for our upcoming remodel and have had no problem keeping the shower curtain inside the shower. The inside of the curb is 4".

For the remodel, we're planning on a Kohler cast iron shower pan. They are raved about here. I had considered a shower curtain and it was pointed out to me that a curtain with magnets in the hem would help keep it in place. However the inside curb isn't very deep and though I think it's doable, we liked the look of shower doors better. You are looking at a greater expense with tiled walls but you'll be able to get the type of grab bar you want.

The existing bath tub is rectangular, about 41" by 60". There is a wall behind it and walls at the right and left. It was probably installed in the 1990s and is made of some plastic-like material, including its back and side walls. These walls are a bit flexible. I don't know what's behind them... we're hoping it's not ruined tiles.

I am in the middle of my second bathroom remodel. 2 different bathrooms. We remodeled the hall bath for my aging parents who needed to move in with us. We removed the shower/tub combo that was an original 1970's install. We used a contractor and had a new walk/roll in shower (curbless) with bench and 2 different shower heads installed. It has a glass door. It worked great for my parents and did not change the foot print of the bathroom or previous shower/tub. It did require a complete gut and rebuild including the plumbing and drain location. It is tiled so that was also an expense. We installed blocking in the walls and grab bars.

We currently use it daily as my Mastr bath is now undergoing tub removal and shower redo. We want to age in place so we are adding blocking for grab bars where we will need them later but not installing them. We planned for door swing, wheel chair access, and the space for someone to assist with bathing if needed. We do not have mobility issues currently, but I have broken a knee and an ankle and needed to rethink the shower. I highly recommend a built in shower seat and hand held shower head in addition to a regular shower head.

This is a personal choice for both aesthetics and cost. I prefer a tiled shower and did not research preformed showers. Not sure how you would add grab bars to a preformed shower later as I think it would compromise the waterproofing. I consulted ADA guidelines and only installed horizontal grab bars in the shower and by the toilet, 1 in each place.

Good luck, hope this helps.