To be bamboozled by mattress choices (for child)

[Drummingisfun]

My five year old is going into her first single bed, we've got a base already but my head is spinning from all the mattress choices.
Back in the day it was a sprung mattress but now there's soooo many options, like Simba, Caspar, Emma, LaLa, Dipsy...
I don't even know where to start.
Should I just get a cheapy one or is it worth spending a bit more?

I'd get a relatively decent one if you're talking full sized. Not super top end, but a cheapy one could just lead to back pain and such in the future.