Hi Craig.

Thank you for your question.  Remember, in general, pocket springs are usually 6" in height plus a minimum of 2" compressed wadding each side will give you a mattress that will be 10"" [20cm] in depth. In your case, this will exceed the mattress safety depth required for bunks. Budget thin mattresses are just plain cruel to inflict upon a child.

Consider a foam mattress (made flame retardant by law in this country) this will be infinitely more comfortable than a cage sprung matt thin enough for your requirements and as your kids will not be in bunks for too long it seems unnecessary paying out more than you need. Alternatively, purchase a budget matt [for the support] but invest in your own comfort layer (topper) to give the comfort that will most certainly be lacking in the budget matt.

Finally, never disregard the safety element [height] of the mattress plus topper you will eventually use on the bunks.

Hope this helps and feel free to call the office on 0161 437 4419 for any further information.

Kind Regards