Blanket size for a yearling?

I searched for an answer to this on the forums, but didn't see what I was looking for so I apologize if this has been asked before...

I've got a yearling who's about 17 months old. I live in VA and while it doesn't get terribly cold I like to have a midweight for when it gets into the 20s and below, and a sheet for the late fall/early spring when it's raining and chilly. I know it's more my neurosis than my horses really NEEDING one, but it makes me feel better ;)

Anyhow, I grew up in California and buying blankets is a relatively new experience in my world, haha. For youngsters, about how much larger would you suggest going in blanket size?

He measured at 70" the other day, and he's about 14 hands. I expect that he'll end up around 15.2 hands + when he's fully grown (both mom and dad are that height). I'm just trying to guesstimate how much I should add on to the blanket to at least make it through this winter! Any experience or suggestions?

If he measures a solid 70", then I would order a 72. It won't be so big on him to start, and won't end up so short by the time you don't need it anymore. He might have some hiney sticking out by March/April, but that's ok :)