For the best help

Post a scaled drawing of this bath.

That means every solid inch of wall, every opening, the window, entry door. Every inch of it, just as it is now.

Pretend this is a bath, not a kitchen: ) example below

Graph paper is fine, neat, use a ruler bold and legible.

That is the BEST method for good advice, and note if you are on slab...or crawl, or basement foundation

The technical issues with keeping a window in the shower are all resolvable with a large enough budget to handle them. Windows are not meant to be waterproof from the interior, and are not safety glass, when from that era.

What is the motivation or goal for the remodel? Bigger shower? Tub leaking? Better window views?

A floor plan is always needed when requesting help with relocation of showers, tubs, etc. Please provide so we can better assist.

Which would you use most? Even though i don't use it daily , This old body needs long soaks in a tub.

"Were struggling, I'm conflicted, we're in our seventies......we might have to, our builder suggested, we have a new mid century style vanity........"

What WE don't have is the extremely accurate , 2 dimensional , drawing. The one that shows every solid wall, every window, every jog, turn , opening and the dimensions for each of those.

You can get the"builder" to do that drawing to 1/4 or 1/2 inch scale ( even better ) .

He notes the plumbing locale, especially toilet soil pipe.

If we had that, we might even be helpful "designers" .......as builders and contractors are not "designers" : ) They are technicians, You are in fact the "designer", unless you hire same.