A Separate Shower and Tub, or Just One
The Space Arithmetic
A comfortable shower enclosure and a freestanding tub together need a substantial footprint plus clearance around both. Squeezing them in produces a shower too tight to turn around in and a tub with no room to step out of, which satisfies a wish list and nobody using the room.
What Gets Used
Households that install both frequently report the tub going unused after the first year. That is worth knowing before allocating a quarter of the floor to it. A large well built shower with a bench and a decent valve is used twice a day and is the better spend when space is finite.
The Resale Argument, Examined
The common claim is that a house needs a tub to sell. The accurate version is that a house needs at least one tub, somewhere, for buyers with small children. If a hall bathroom has one, removing the tub from the primary suite costs nothing at sale and buys real space.
Freestanding Tubs Have a Catch
They look uncluttered and they need a floor mounted filler or a wall mounted one placed exactly, they need the floor beneath checked for the loaded weight, and they leave a strip behind them that is awkward to clean. None of this rules them out, but all of it belongs in the plan rather than in the surprise column.
A Middle Route
An alcove tub with a good shower over it, done properly with a solid surround and a fixed glass panel rather than a curtain, remains the most efficient use of a modest primary bathroom. It is unfashionable and it works.