Tbh I've had smart stats for the last 5 years and just seemed the option to choose. Didn't really think much into not having them. Also I was surprised at the cost as I expected it to be much much more. I had a set up quoted with Warmup and that came to over £3k, hence being surprised.
Wunda have stated a minimum of 50mm insulation board but if we have space to go thicker then do so. So I'm aiming for 80mm boards which I'll sit on ply which in turn is held up by battens.