That sounds much too high. My current tub is 14 inches and I would not want to have to step over anything higher than about 16 inches. I think stepping over such a tall tub would create a serious slipping hazard.

Whether you sit down for a bath or stand for a shower, you have to get into it and out of it the same way.

Are you going to have any grab bars nearby? That would be important for safety either way.

But with our deep tub, we are not having a standup shower. It will be a handheld sitdown operation, yet we will still have to get in and out of the tub safely, by standing and holding a grab bar.

If you have not closed in all the walls surrounding your freestanding tub, be sure the contractor adds blocks behind the walls in the appropriate spots to securely mount grab bars in several positions.

I would think the width of the tub is more important in determining whether you can comfortably and safely stand up for a shower in your tub. Since ours is a clawfoot slipper tub, we omitted a standup shower feature. Even so, we still have to deal with getting in/out of the tub.

I think 24 inches is too high for a tub/shower combo. We have had an 18 inch high tub/shower combo for many years and are looking to remodel so we can have a walk-in shower and a separate soaking tub. If you shower every day you will find 24 inches to be too high. Plus, how are you going to keep the water off the floor? Shower doors, shower curtain?

I am finishing up a main/guest bathroom with a 20" high tub and shower combination. For me and my significant other, the tub height is very comfortable to step in and out, though we are not using it daily. I imagine it would not be comfortable for anyone with mobility issues. I think I would be fine with stepping over a 24" tub, but I can see how it might not work for everyone. Can you mock something up with cardboard at 24" high in front of your current tub/shower setup and try stepping over it for a week or so to see how you feel about it?