When I was young I used to blister a lot, heels, ball of the foot, big toes, between the toes; you name it, I blistered there. Over the last several years I've abandoned my "go as fast as I can" mentality from when I was young, and stared concentrating on LSD (Long Slow Distance). Why is this relevant? This year is a good example; prior to July, I had never run more than 170 miles in any one month (and that 170 mile month was done back in 1979), however, in July I ran 218 long and very slow miles (it was really friggin' hot and humid around here in July), and with a couple of very minor blisters between my third and fourth toes on both feet (easily remedied by rubbing petroleum jelly between the toes before each run), I had no blisters. What I attribute the lack of blistering to is all of the long slow miles which have significantly toughened the skin on my feet.
In September I got recruited to run on a 6-person Reach the Beach relay team as a very last minute replacement (all of two days before the event). Even though my five other team mates had been working toward this 205+ mile relay for some time, and, in theory at least, had been training for it, I was the only one who finished all six legs (totalling 32.8 miles) with no blisters.
Long story short, let your feet heal up, and then start running at a slower pace than your used to and then start extending your miles. As a side benefit, once your feet have toughened up, the rest of your body will benefit from the extra miles as well and I predict that your half marathon times will come down significantly.