Where do you get sheets for 126x63cm (size 300) cot mattress?

[PeachyCobbles]

Hi, hope a question about sheets isn't inappropriate for the "sleep" topic (I'm new to Mumsnet and haven't seen a "things to buy for baby" type forum on here).

I have been given a cot (an old mamas and papas one I'm guessing) that fits a 126x63cm/"size 300" mattress for my first baby (due imminently). She'll be sleeping in a bedside crib for a while anyway, so getting sheets/mattress for the cot is not the most urgent thing in the world, just thought I'd look into it now.

But fitted sheets all seem to either be 120x60 or 170x40cm - what did you guys with the weird mattress size do? Buy sheets too big, use non-fitted ones, source specialist ones to those measurements? (am worried about wrong-sized ones slipping off and getting tangled, but can't find 126x63 ones anywhere, not even on mamas and papas own website).

I think I’m reading these measurements right but I’m tired so not sure if I’m missing something obvious.

https://www.amazon.co.uk/Organically-Antibacterial-Hypoallergenic-Eco-Friendly-Biodegradable/dp/B08H1GGL52

https://www.cotmattresscompany.com/products/copy-of-100-cotton-fitted-sheets-cot-bed-white

Thanks for having a look for me! I'd seen those already but the Amazon ones are not available and the others are £15 a sheet which seems insane and is more than I pay for our adult-sized bedsheets (although I suppose I might have to just suck it up and go with them). I was hoping maybe some parents who have used this size mattress themselves might know of somewhere I hadn't spotted with a Google search.