You need to buy the 'deeper' sheets- target sells them.
I think they're 60 CMs deep from memory.
Ah, I never knew they existed! I'll be searching for them when I'm next at the shops. Cheers!

Olive, glad I'm not the only one with this issue. I'd thought about buying more expensive ones (like Sheridan) to see if they were any different but checked the measurements on the various packages and they're all the same. These deeper ones Emma has mentioned sound perfect. I looked into a super king too but I think they'd be too big.