Bugger, I feel...........................buggered................
The prices on AliExpress are always well worth checking. Especially if you aren't in a rush for the item. As delivery can sometimes take 3-4 weeks but usually it's approximately 7-10 days.
Just remember to add 20% vat to the prices quoted. Even then you are usually guaranteed to save at least 50% compared to UK prices.
Ironically, items seen on UK eBay & Amazon etc are often purchased in bulk from AliExpress by amateur sellers. It's very easy to negotiate bulk discounts with the Chinese sellers. Then add on an amount that will still seem cheap to a UK buyer.
Hey presto, a quick & easy profit!
Let's face it, the vast majority of stuff these days is made in China. So much so, it's extremely hard to avoid purchasing Chinese made items. So why not save a load of cash by purchasing from as close to the original manufacturing source as possible. I'm sure the manufacturer would deal with you if you were ordering 500+. But the AliExpress sellers will happily offer discounts on already cheap items for orders of a handful of items.
You could return your heated waistcoats to Amazon for a refund saying they don't fit. Then re-purchase them from AliExpress. That might sound slightly inconvenient, but according to
@Scrappy's figures you'd save £62 in the process.