Physical stores that sell short single/odd sized mattresses for a child?

[0nesie]

I am looking for a new mattress for my son. He has a bunk bed which is a short length (but normal single width) so I need a mattress to fit 90 x 175cm. The current one he has is an open coil one that is really really uncomfortable (you can feel the springs through it). I am on a budget (£150 or less). Are there any retail stores that sell odd sized mattresses that he can actually test in store? I know I can buy a mattress online but don't want to risk buying a similarly uncomfortable one. He is a bit of a sweater and very skinny so not sure if a 100% memory foam would suit him but maybe something with some memory foam padding on the top. Any suggestions welcomed!

My mum has an odd shaped bedroom and the layout means she has a custom made bed frame. I think it's 4 feet wide by 5 feet long so she has to have mattresses made specially.

Have you tried google to see if there is anywhere local that make mattresses. They would most probably have a Showroom and you could try the mattress and ask them to make one like that but to your custom size

Alternatively buy a good quality mattress topper. We didn't realise how rubbish our mattress was until I washed ours and couldn't get it dry in time for us to go to bed. It was One of the worst nights sleep of my life (and I have children)

Thank you. I think the mattress topper is the way to go for now.