Safety by the pool

[Nomorerain]

Hi,
Can anyone please advise me what would be the best thing to buy for my 2.9 and 1.7 yr old DD's to keep them safe by the pool on holiday? Obviously they will never be left alone but we're staying at a villa with a private pool so I want to make sure they're absolutely safe. I wondered whether the jackets with floats in them might be better than arm bands?

jackets with floats I think (FWIW) would be safer and also more comfortable (unless it's scorching hot) and also, perhaps most importantly, harder for them to take off themselves (the zips usually have little catches at the top).