Nikola, I have a blue one that dd has outgrown and was about to put it up for sale on here for £2.00 + postage if you're interested. It says age five on the label but unless your three year old is very tiny, I'm sure it would fit. My dd is still only four, though a tall four iyswim. It has a zip and poppers and is sparkly and has warm fleece on the inside. Only thing is that part of the bottom popper is missing - I'm sure it could be replaced, but we never did as we just used the zip. Having said that, she's only worn it a handful of times, so apart from the popper, it looks like new. Will hold on to it rather than advertise it if you'd like it.
Funnily enough, she also has a pink one the same which fits her now. It says age eight on the label! She doesn't often wear it, but will hang onto it for now just in case she takes a notion! Will email you tomorrow as have parents here now and are about to go out, lol. Will also weigh it and see what postage will be. It's fairly light though, so not too much.
WWB - got your cheque today (thanks v much), so will get onto that after my folks return home!