Advice on buying a blanket

I know that it doesn't get ridiculously cold down here in Georgia, but I have a blanket for my mare Ginger and I'd like to buy one for my pony, Duncan. I borrowed a tiny one from my mom last winter for him, but he's out grown it (he was actually getting too big for it by the end of winter).

I know how to measure for one, but should I get one that's slightly bigger to accommodate his growing over the winter? He's a year and a half old and is 10hh. I don't expect him to get much taller than that, maybe 11hh, but I don't want to spend money on a turnout blanket only to have him out grow it.

Do you feel he must have a blanket? Whereas I blanket my TB as soon as it starts getting chilly (he's currently wearing his insulated rain sheet at night), i'm pretty sure my colt won't be getting any type of blanket or sheet this winter. He's already getting a really nice winter coat in, and with proper feed and shelter I have no worries about him staying comfortable and healthy this winter.

If he's only a year and a half he'll probably still grow a bit and he'll be filling out for quite a while. For this year if you buy him a new blanket I'd maybe go for the next larger size. So, if he measures 54" then I'd maybe buy the 56" blanket and see if that keeps him all this year and maybe into next. I try to do that with my horse foals and some years I get lucky and some not so much. What it ends up meaning though is, I have 50 plus blankets in varying sizes. ARRRGH!

Crimson- My horses are just pasture boarded, and there's not a shelter for them to get under if it gets bad out. Last winter we had a couple showers of freezing rain, and then snow as well. My dad thinks I'm ridiculous for wanting to blanket them at all, but I usually save the blankets for just the worst of winter. I wait till they get a decent coat in, then just put the blanket on at night or for bad storms.

Dreamcatcher- That's what I was thinking of doing. Just wasn't sure if it'd be a bad idea to buy one that's a little too big. Thanks for the advice!