Mattress compatible with Ikea Stora Loft bed?

I am looking for a mattress 140cm x 200cm to fit an IKEA stora loft bed. Do you offer these? What kind of price should I expect to pay? We have an artisan I think (Superking size, cost about £2k I think). But this is for my daughter. I would like it to last her for the next ten years or so.
Thanks,