This may already have been posted - ive not read thoroughly - but a cheap alternative that definitely works is to buy a large microfibre towel - I get mine from amazon - bathsheet size, wet it in cold water, wring dry - and it feels dry ( bit like a large chamois leather?) but cold to lie under. And it stays feeling cold till it dries. Honestly - it’s a life saver abroad, but increasingly here too !!
The media are already after Andy!
