Oasis jumper sizing

[Littlemiss74]

I've seen a jumper in Oasis with 20% off that I like but I am in between the size S and size M. The S looks like it fits better across shoulders and arms but is quite tight across chest and middle. Not sure which to go for. It's a short style jumper not a long style.
I'm a size 12.
Anyone got experience with oasis jumper sizing please?

I am a 10 with no boobs and normally go for a small in Oasis. There isn't much extra room so i would go for the medium. I find oasis on the smaller side to places like next.

If it's a short style I would go for the medium. Isnt there an extra 29% off sale items online til the end of today?

I bought a jumper from Oasis last year and it was generous to start with, but after a couple of washes it was huge. Don't know if that helps or not...

I find oasis really short in the body so tend to size up. I’m only 5ft but still find them short!

Thank you everyone. I think the small looks a bit of a better fit but feels tighter so i think M might have to be the one.
The 29% is just on sale jumpers i think which unfortunately this one isnt.