LikeaSoul - yes we do - have tried adding a lot, a little, etc., nothing makes me comfy.
I am going to try DH's old foam thing. I have always coveted Thermarest Neo Air or whatever they are called. I am not buying anything else unless I see it in the flesh though.
Sobek - my idea is to put the 5cm double on top of the two 10cm singles and then use a fitted sheet to hold them together.
You can buy 'coupling straps' and thermarest make this
www.facewest.co.uk/Thermarest-Down-Coupler.html?gclid=CLKJ8evep8YCFYoBwwodsCQABg
but it gets a few rubbish reviews.
Not sure what the answer is. I don't want to buy another, more expensive, swisher SIM tbh as I think mine should be decent enough.
Have no problem with spending money, just hate wasting it.
I know that air beds are not the in thing these days but I have been camping since I was 20 under my own steam (nearly 50), and have always been absolutely fine on a decent air bed. This tipi tent we have bought for weekends really needs SIMS, we can stack them during the day and will probably sleep separately when we have a fire inside.