My booties are 5mm and quite old, but not very thick for 5mm boots. Anyway, I will have to make do.
In regards to spin out - On my 6.5 sail and up, I have adjustable harness lines, so no extra pressure on the back hand. I do have the booms pretty high, so I may try it a little lower. My lines are pretty long too, carry over from Formula.
Given all my formula sailing, I am pretty used to a lot of back foot pressure, so I think I just have to make the appropriate adjustments to avoid spin out. Where I have been sailing, it's pretty choppy and the board gets a little air quite often, so with the normal pressure on the back foot, I frequently get spin out. Again, just have to adjust to the new board.
I have to admit that I have never been comfortable getting into the back foot strap of any board while bearing off after a jibe. Mental issue with getting launched over the front of the board with all my weight on the front foot.
Regardless, thanks for your suggestions.