Glad the threads you read were of help.

Easiest, and often times the most user-friendly, is two supply valves, one for each head. With two bathers, each can select their own water temp. In general, that can be achieved most economically by using two two pressure balance valves at an economical price.

Diverter valves and their trim can often be as expensive as a supply valve and its trim. Obviously you can price things out through the manufacturer of your choice:

-Two individual supply valves and their trim.

-A single supply valve and its trim plus a diverter and its trim.

When you get into diverters, then you have all sorts of choices...the diverter can supply one head OR the other, but NOT BOTH simultaneously...OR it can supply one head OR the other, as well as BOTH simultaneously.

As you wrote, with a PB valve you may not get temperature control at any volume. Volume control at any water temp can be of value, it depends on how you use your shower. To do that, you're right, it can be accomplished with a thermostatic valve. To be fair, there are some PB valve that offer that as well, you'd have to shop around to find one. But for the most part, PB valves at low flow will only give you cold water.

My own shower, we have two PB valves that supply two individual heads. I do like the ability to have different water temps out of the two different heads.

You're certainly on the right track. It's simply a matter now of balancing features versus budget, etc.