I'm not going to suggest you shouldn't buy one - and hope you get some good suggestions, but as an aside there are a couple of things that you can buy in a motorbike shop that will make a big difference.
The first is a really good pair of gloves - I use a pair designed (I was told) for moped riders, which lack the (irritating) kevlar armour that you get on many motorcycle gloves, but are still extremely warm and (just) thin enough to operate switches. These can be supplemented with a pair of silk inner gloves from the same source.
The other is a thin balaclava designed to go inside your helmet - your head is the single biggest source of heat-loss and this makes a huge difference.
But, Irvin jackets are wonderful things, and I'd not be without mine! There are various patterns available - some more authentic than others. I would recommend getting one with a reasonable flap across the front to avoid drafts, and a strap and buckle (there are usually two) across the collar so that you can have that up around your chin - otherwise the cold drafts around your neck are horrible in some open cockpits.
G