(Image credit: Future) Hot summer nights are coming, and if you're already dreading their impact on your sleep then a cooling mattress could be your wisest purchase. Now is a good time to buy too, as the Avocado Green mattress, now $2,039 for a queen with 15% off at Avocado , is on sale. We awarded this supportive organic bed full marks for cooling comfort and recommend it as 'hot-sleeper safe'. The Avocado is our top-rated organic mattress and when it comes to full-body support, it rivals even the best mattresses you can buy online . It's also ideal for summer, thanks to a breathable build that banishes night sweats. Sleep cool on hot summer nights (Image credit: Michele Ross) Summer is on the horizon and I've already noticed the effect of warmer nights on my sleep. And with the Farmers' Almanac predicting hotter than usual summers for most of the U.S., you can expect some stifling weather ahead.…