I'd use the same type of drain that I would for a laundry tub, with a stopper.

better to ask on forum with real plumbers?
no overflow seems risky.
if the drain hole in tub bottom is close enough to a sidewall of the tub, i wonder if a doorknob holesaw can "bore" (but tub finish may chip) a hole into tub sidewall for overflow?
without overflow, I'd want a floordrain nearby. and maybe recess the floor under the tub? OTOH, an accidental flood shouldn't be so disastrous if this bathroom is on garage slab floor that drains out garage door.

The make a special drain assembly that has a standard tub shoe under the drain which is connected to a tee on the drain line. On the top of that tee where there would normally be a riser for the overflow there is a removable cap that is used as a cleanout.

Thank you all for the ideas. We'll look for the special tub shoe.

And, yes, we are considering a drain with a stopper rather than a life-and-turn or toe activated mechanism. Given that, having the cleanout as part of the special shoe might be a good bonus.

You need to use a WATTS "Female Standing Bath Drain" also called a standing bath waste pipe. Basically the assembly connects to the drain hole at the bottom of the bathtub then a connecting pipe runs at a right angle under the tub and floor about 8 inches past the side of the bathtub where it dead ends on a horizontal to vertical (up and down) T connection. Below the T connection is the trap. Moving up from the T connection there is an inner and outer standing pipe with a cover that allows one to pull open or drop closed the inner pipe which effectively opens and closes this type of bathtub drain. Overflow is controlled by a hole on the top side of the inner pipe. When water reaches that hole it flows in and down through the inner pipe to the trap below. I hope this was helpful.