I've looked online at the Gelert xpedition double, Vango double and Outwell. Can't affored thermarest or airics. Is the 5cm thickness better than the 3cm? Vango is shorter and narrower but deeper, whereas gelert is apparently from the same factory as the 'market leader' (Thermarest??) but only 3cm deep. also, people are saying they slip off them - how essentail is the non-grip thing? Off a week on Sat. for a fortnight with our 4 DC and a dodgy leg/ hip problem so really need to sleep well! Thanks.