@Anna9170
I'm no expert in mattresses. I didn't have a huge budget whenever I have bought them for the guest rooms, but did not want to buy cheap, nasty ones either as I think it's a false economy. So, I bought some of the lower priced ones from John Lewis as I've found their products generally to be good quality for the price.
I agree that mattress (and pillow) protectors are a must. It's annoying to have to replace spoiled bedlinens, but spoiled mattresses is another matter! However, they don't add much in terms of comfort, whereas the extra thick mattress toppers have really transformed my beds. Since I got them, most guests rave about how comfortable the beds are now. Even those super fussy guests who complain about numerous things admit that the bed is very comfy!
The toppers I bought are from a company called Groundforce, but I got them discounted via voucher deals. Unfortunately, they are difficult to fit even into my 8kg washing machine as the are so thick. A trick I learnt though with bulky bedding is, if you have a bathtub, first soak the item in the tub, wring out as much water as you can and then it fits more easily into the washing machine. I did this recently with a very thick Superking duvet that I had never been able to fit in the machine before.