IKEA Kura bed - mattress

[Greentomatoes21]

My son's room is very small. We would like to get him the kura bed to offer more play space underneath.

I have read many reviews of the "related products" mattresses on the ikea website and they seem to be problematic. 1) Too small for the bed, despite being described as having same dimensions. This apparently leaves a gap so the mattress can slide around. 2) generally uncomfortable because it is just foam and is thin (to allow for the side guard to be correct height to stop them falling out).

Mattress needs to be:
90 by 200cm
No more than 5.5 inches deep

What mattress are people using successfully with this really popular bed?? Please help!

We are in the UK.

We had a Kura bed for years and used a normal mattress without any issue. The small gap is great for stuffed toys!

Oh thanks so much for reply. Was it an ikea mattress you used?

We got a euro mattress from Amazon. Fits perfectly.

Thanks! We have used our own mattress, which is a tad too short but we have filled the gap with teddies as a pp suggested! We have also installed a little bed guard we had and it looks great and more importantly is safe. Thanks all!