well, whatever rides you do, short long whatever, do get a modern helmet. When I had my first helmet around 20 odd years ago, it was way ahead of the old Bells for ventilation. Nowadays, very affordable ones (like $20) offer waaaaaaay better ventilation than my first one. I have a med priced one, about $50-60 and even in hot hot weather it is just fantastic, plus the visors on helmets really help with sun also.
Getting back into biking is great, take it easy and regular rides of even short lengths will be fine for getting back into biking shape.
all the best
My brother and sister-in-law bought me a great, new helmet for my birthday with blinking rear, red lights no less. It's a Bell Arella (and your absolutely right about the visor). I did a 41 mile, "hill"ish ride the other day and felt completely recovered the day after, although I take the hills real slow and in the lowest gear.