"...our builder suggested...getting too cold". And that's the issue with doorless showers. You can make it warmer with in-floor heating, specify Schluter Ditra-Heat, all others are cr*p. A friend had her heating extended from the shower floor up the walls 24 inches for extra heat (northern Montana). If possible, a wider shower is preferred...48 inches or a little more.

We have one in our basement bathroom... it's the bathroom our 3 teenaged boys use, but hubby and I use it sometimes too to make sure everything's working well and because it's nicer than ours (we haven't done the master yet). We really like it! I was afraid it would be cold because 1) it's in the basement, and 2) we didn't use a heated floor. But we find that the area heats up very quickly and I don't feel the least bit chilly using it, even when sharing... and we didn't go with dual shower heads. (We did go with a rain head shower though. It has a hand held, but you can't use that at the same time as the main shower head, it's either/or.