Planning a large shower for use by seniors requires care - think non slip floors (solid shower pans usually need anti slip mats which take away from an upgraded aesthetic) grab bars placed appropriately, plumbing and product storage located near seating. 48x60 may be too large once you get into the nitty gritty planning as a wet body needs to walk farther to exit - which can be dangerous. I’d suggest a certified kitchen and bath designer help you as this is a life safety concern.

Also large showers can feel cold and drafty so a heat lamp in the room should be factored in - again- back to the recommended pro that creates a plan for you. Then you pick out the finishes. Don’t work backwards.

I just got same advice. I'm going to settle on 24x48 ceramic tile.gorgeous .not worried about grout as soo thin.im using countertop similar to this pic.flooring just using hexagon white. Quartz counter is silestone et noir

Have you looked at Wilsonart Wetwall?

https://www.wetwall.com/

I would avoid a black shower as well. Not just because of the daily cleaning to keep it looking good but also because it is harsh and because it sucks light out of a room. Bathrooms need to be well-lit and doubly well-lit for aging eyesight.

I like to know with whom I'm showering. Black camouflages spiders and ear wigs. Not on my wash.

Honestly you are seem to be omitting the most critical element of the design - how it functions - especially for seniors.

I designed my shower with a view to aging in place so I designed my shower so that it works for a senior - and I also then designed it so that it is a gorgeous tiled shower

Even if not curbless, have as low a curb as possible so that it is easier to step over the threshhold

Have grab bars at the entrance to the shower as well as along the back. Mine are oiled rubbed bronze like the rest of the hardware and so not unduly institutional

Have a built in seat because it is necessary if one comes back from the hospital and also wonderful as one gets older and perhaps wants to sit and relax if legs or knees are painful. Sitting on a comfortable bench in a deligtfully warm steamy shower is wonderfully relaxing.

I have two hand held shower heads and one is by the bench so that I can easily access it if I am sitting. My designer and I joked that it will be great when my attendent needs to hose me down :-)

A built in bench is better than a free standing one becaue you don't have to clean around it and it doesn't take up floor space. If you really need a bench you a stool isn't going to work because you need the safety of having a back.

It goes without saying that you need a non-slick floor for both the shower and the bathroom. I rented a place while my remodel was being done which had 12' x 12" slick tiles and the slightest damp on my feet could have meant my lying dead on the bathroom floor because they were so slippery.

While most seniors aren't going to wind up in wheel chairs, it is entirely possible at some point they might need a walker so make sure that there is sufficient space to navigate in one.

I added a sit down area at the bathroom vanity in lieu of a second sink. This means I can comfortably sit while doing making or drying hair or other grooming stuff.

And good lighting. I have lights in the bathroom which are on motion detectors. This is required in California for bathrooms but it is also a good safety measure because navigating in the dark - especially for seniors is not a wise move.