Well, given that we're talking only about a 2 mile each way ride, I'm inclined to say just ride it. But, given that you've got a balance issue, I'd say to consider the route through the village you need to take and whether it involves multiple stops where stability when stopped may be a problem. If you're rolling, I'm guessing you'll be fine, but if you're perched up on one tip-toe at a light, perhaps after a vigorous effort or on a breezy day, it may be a prime condition for the balance thing to cause a fall. Perhaps you could get accustomed to dismounting and standing, but if the seat is slammed to the frame, you've probably got no stand over, eh?
So there's no question that a smaller frame would be more appropriate, however, I wouldn't let the absence of that stop you from riding. Plenty of people ride around on too big bikes, and probably most of us, when we were kids, were too eager to get on our parents' bikes, but did that stop us?!
Also, I think the approach to start gradually with the ride to work and build from there, without too much "hard target" expectations is a great way to ease into cycling again. Once you've got the wind in your face again and feel the thrill of gliding down the road, I'm sure you'll start thinking more about where you want to take the sport/hobby, about what your needs will be, and what kind of bike would suit you best.
Bon chance!