Your safest bet to get what you want would be to go with a thermostatic valve. Some pressure balance valves will do what you want, some won't.

I wanted that too llemay so I bought the Delta Monitor® 17 Series Tub and Shower with In2ition® Two-in-One Showertub and shower combo. It's not installed yet. You can set the temp independently from the on/off/pressure. Notice the two handles on the control valve. One is for on/off/pressure and the other sets the temp. When I was searching for the differences between pressure balanced and thermostatic, it basically came down to "will you have 2 shower heads (in the same shower) being used at once. If so, buy a thermostatic valve.

Monitor® 17 Series Tub and Shower with In2ition® Two-in-One Shower

I'm no plumber, but we had the same objective. I think what we used was the thermostatic. There's a diverter that switches just between the rainhead and the handheld and the temperature remains the same as where you left it. It's a Hansgrohe system with an "ibox" whatever that is.

I have to admit, the rainshower is nice, but I could easily live without it. The handheld is very satisfying and it would be fine just to have that. You do have to be a little careful about standing under the rainshower when you divert it to that-- there's a pipe full of cold water that's going to come out first!

We got the thermostatic based on the salesperson saying that she couldn't live without hers. My DH loves it and uses it like you are planning. I'm not so thrilled with it because I like to be able to get really cold or really hot water in the tub/shower and find that we can no longer do that - I asked another salesperson about this and she said it was a drawback of the thermostatic systems (but not sure if this is correct of all thermostatic - ours is Grohe).

We're using a thermostatic valve with a Kohler hydrorail, it's a very elegant solution for a fixed and handheld shower with a built in diverter.

We recently installed a Delta In2ition rainfall and handheld set up too. We like it a lot, but have had continuing problems getting hot water to come through

Based on all the review comments I've read (here, on Amazon, etc.), the valve is a little tricky and the plumber's competence may be a factor. We've had to call him back several times to fine tune the temperature limiter position and some other issues. We hope to do some work on our other bathroom this fall. We'll get our reliable plumber to do that work, and also check on the master bath problems (contractor selected the plumber who can't get the Delta fixture to work) All in all, we really like the In2ition system. Just be sure to pick a good plumber!

Whew! I was hoping I hadn't made a mistake ordering the In2ition. DH hasn't showered in nearly 10 years, he's a soaker, so I didn't worry TOO much about a shower head but wanted a nice one (just not a spendy one). Now he's decided he wants to go back to showers again....after I chose a black porcelain and cerma marfil for the surround :( He better learn to use a squeegee on that black tile! <g> We have a super plumber :) Plumbing is the one thing DH won't touch.

Hi llemy! Check out our blog post from today to help you determine which type of shower valves and controls are right for your bathroom. Please feel free to contact us if you have any questions. http://blubathworks.blogspot.ca

Blu Bathworks, I read your blog. I have a pressure balanced system but can adjust my water temp and never touch it again (if I choose). Another handle adjusts the flow rate.