C10 250,
I have searched ad nauseam for IWBs with thumb breaks and can tell you that your choices are extremely limited. If you are willing to get a non-tuckable IWB with a thumb break, your choices will widen, slightly.
The holster manufacturers that I contacted (like Comp-Tac) won't custom make one. Raven Concealment wasn't too enthused to make one for me and quoted $150. I believe that price is way out of line, and after reading reviews of their holsters, I see that the kydex tends to crack/break. Also, their holsters take up a lot of real estate.
Andrews Gun Leather makes a leather IWB w/ thumb break, MacDaniel II, but the photos show it riding too high for me. They might be able to customize the ride height.
Eagle Industries makes a non tuckable IWB with a thumb break that's decent, but they raised the ride height on their newer IWBs and are too high for me.
Milt Sparks - the only experience I have with them are from two LEOs who used the same range as me a couple years back. They got Milt Sparks OWB holsters custom made with thumb breaks which tore off within two weeks of receiving them. One fellow had a second one made, which also tore promptly.
Take a look at the Don Hume Strike.
IWB STRIKE [IWB Strike] - $67.00 : Don Hume Leathergoods, manufactures high quality leather and nylon goods.
I have one. It fits your requirements, but not sure if they make one that fits your 6906. I would definitely call them to see. I think they give cops a discount. My opinion on the Strike is that the ride height is good - just high enough over the belt for your hand and fingers to get a good purchase on the gun before you begin the draw. You will have to thread your belt through the kydex belt loop. The thumb break is easy to work and really not an issue with some practice. The leather is duty grade making the holster a bit too wide for IWB, and it may colapse too much for one handed reholstering if you cinch your belt real tight. Also, another thing about all Don Hume holsters that I have observed is that the straps that go over the hammer tend to crack a bit after about a week - the leather doesn't rip, but the finish cracks a lot.
Also check out Fist holsters, they have a great reputation, and you have the option of purchasing with a thumb break. I have no direct experience with their products, but I called them and they politely answered all my questions.