Plastic mattress protectors - safety

[DeepDeepFlavours]

My 6.5 month DS has occasionally vomited/poo-ed when in bed and it has gone onto his sheets and through onto his mattress. I bought a mattress protector from Ikea that is cotton on one side and plastic on the other however the instructions say to only use at the foot of the bed due to danger of suffocation.

DS moves all round the cot in his sleep and obviously vomits from his mouth so it is useless if I only cover the foot of the cot.

Does anyone know if it is dangerous to use the mattress protector on the whole mattress? I've looked on the Internet but can't find anything about the risks so maybe Ikea are just being uber-cautious to avoid litigation? Does anyone have any advice please?

I have one which is a fitted sheet so obviously goes over the entire bed. I reckon they are just covering themselves.

is it a breathable cover? If not then maybe thats why they see it as a suffocation risk. Could you get an alternative one that is waterproof but also breathable? My mattress had a removable washable top cover so when there was an accident I washed the cover and cleaned the mattress (which was waterproof) with a disinfectant solution.