Double Mattress recommendations for side sleeping teenagers

[Abkbjbjb]

So as per the title I have just got my 15 and 13 year old boys a new double bed as they have outgrown single, now the chore of researching a good mattress!! Have looked at a couple of Ikea ones and read some great reviews then some awful ones! So back to square 1, they are both side sleepers and want something squishy lol!
preferably under or around £200

FWIW, you can turn a crap mattress into a great one with a memory foam topper (10cm or more).