We went through a similar search, so I hope this helps.
We wanted 3 devices, but also wanted volume (pressure) control and the ability to leave the temperature set between uses. I don't know if this will suffice, but Grohe makes a few that may fit your needs. The valves and the thermostatic element are in one housing.
An example is Grohe Grotherm 2914200
I'll try to explain below, but Grohe has lots of sales propaganda & videos to explain better.
It has 3 buttons, one for tub, shower, hand-held- or any combination of "on at the same time". Or, any other devices, including Grohe's rather odd two-in-one shower head.
The On-Off for each device is a separate push button and the volume (pressure) for each is set by turning that button. Temperature is universal for all three. It is dialed in with a single knob and can be left as-is between uses.
The installer can set the temperature stop of the knob at any given number. (For example: 100 degrees-F). But, there is an override button the user can push to turn the temperature higher while using it. I set ours to my preferred temp of 104-F without pushing the override. Pushing th eoverride & turning gives hotter water.
It is thermostatically controlled, so if someone uses water in a different sink, the temp at the shower stays the same. (We tested and it works instantly. Never noticed the other water was on.) Downside? Thermostatic elements costs more. Upside? Lifetime warranty & free shipping.)
The device gets mounted in a Rapido Smart Box. There are dozens of trims for the Rapido. (Round, square, 2 device, three...)
The box itself is tapped 1/'2" F-NPT so you can use copper, PEX, cpvc, brass, IPS...
Half inch had me wonder about tub filling.
I tested the gallons-per-minute of the 2914200 at 46 psi without shower heads installed: (Most piping is 1/2" Type L copper, but the overhead tubing has a 10" section of 1/2" Type A PEX with expansion fittings. All but two copper elbows are 45 + Street 45. Two are 90 to the side shower. Overhead is straight shot except for a 3/8" offset of PEX to dodge misaligned framing.)
The one we want fast, the tub, gave 5-1/2 gpm through a temporary boiler drain on the pipe. An open pipe or tub spout would
give considerably more gpm than through the globe type boiler drain.
The center (overhead shower) arm was 6-1/2 gpm without the shower head
The left (hand shower) outlet was 5-7/8 gpm through a temporary hose bibb.
(You don't have to put the devices in the order we have them. You can swap around. One gets lots of icons for the buttons.)
The Rapido Smart Box has much higher GPM open-pipe, so different trims than the 2914200 may give more or less flow.
The Rapido was easy to install and came with helpful extras, like a flushing plate and a tile waterproofing membrane. The valve itself was quite confusing until I watched some videos. Then it was easy. (Before looking at the cartoon instructions, look at HandyDadTV on you tube for "We installed a shower" and look at Grohe's video with the happy guy in the blue polo shirt. Then the instruction pages will make sense.)
One Problem: Ours has a Clunk sound when turning water off. After installing water hammer arresters and some calls to Grohe, someone there decided it was the thermostatic cartridge. They are sending a replacement. Installation should take about 10 minutes.
A Hint You May or May Not Like:
I installed the valve with the on-off buttons 35" above the tub floor. It is convenient for reach while showering and while kneeling next to the tub for washing my dog buddy. But, that height also lets one reach the controls while seated in the tub. (Plan B: Want more water in tub while seated? Push the button with a toe.)
I hope this helps.
Paul
