i drive 7 miles each, no problem for the last 7 years. 55-65 mpg. however, when you retire, how many miles a year will you be driving? you might want to consider a corolla or camry. better price, great mpg's, comfortible and last forever.
I'm a low-mileage, occasional driver and find the Pri to be the perfect car for me. I don't have a commute (work from home) and run my errands by bicycle, so the car sees about 150 miles/month. It gets excellent mileage, and if you have to drive a car (although I encourage bicycling) I can't imagine a better one. I've had it since new and plan to keep it 25+ more years. Maybe it'll be my last car--my dream is to be car-free some day. The only time I had trouble with the 12v battery was when I signed up for the Progressive Snapshot program and plugged in their monitoring device. Since the car is only powered up once or twice per week, I often had the red triangle warning light and slow boot-up times. It never refused to boot though. I did plug in a smart charger at times when it wasn't going to be driven for a while. The monitoring device was unplugged a few months ago and the 12v battery's starting to hold a charge better again. I thought I would have to replace it but now it's looking like it's going to hold on a while longer. I highly recommend it and respect your choice--I don't have the purchasing power now that I had a few years ago (swapped gainful employment for a part-time work from home gig and love it!) so anything new is out of the question for me.
If you truely need just a small commuter vehicle you might consider looking for a used Honda Insight.
I travel maybe 5 miles a day stop and go (mostly stop) traffic. Here we have brutally hot (ie, over 90 and very muggy), long summers and brutally cold (ie, below freezing), long winters. I can count on one hand the number of days I don't need the AC (the AC both warms up and cools down the air in the Prius - in the spring and fall it's not unusual for it to kick in to provide both those functions in one day). As is, I get about 38 MPG in the non-winter months and about 34-35 MPG winter.
Let me raise some Red Flags for and against. First of all my instinct is to defend the Honda Fit. The vehicle I currently own and drive. I have a 2010 Sport...and the dashboard is solid. No rattles. Everything else is subjective, Yes the dashboard is plastic, but I love the layout and design. It has some personality. I'd also say, I think the seats are comfortable. As a subcompact, it does have more "road noise" than many. That's maybe it's biggest drawback. But it's acceptable to me. But...that's neither here nor there. You got to get what you want. I "sense" you want a Prius. So let's start with the Red Flags FOR a Prius. I wouldn't let your currently short commute be a big issue. First of all? It won't hurt the vehicle. If you are at all concerned? Inbetwen classes, a few weekends...take a road trip. Secondly? You say 2 more years? Well you never know what life is going to deal you. Maybe in 2 years you'll be needing a more economical vehicle? Right now, you are evaluating based on your short commute. But who knows? Things change. And if suddenly or even by planning, you eventually have a longer commute, it's nice to have a vehicle that routinely get's 40+ mpg. So personally? I wouldn't let currently short commute deter me from buying a Prius...if I wanted one. You might not be able to push the window of routinely obtaining maximum MPG, but you still can't buy anything better outside of a Leaf, Volt or Plug In Prius... Now for Red Flag "bad". Check out The Prius seats. You say comfortable seats are a priority? Again, subjective to the individual, but there have been people that complain about Prius seats...across the generations...If you don't like The Fit seats? You may find you don't like the Prius seats...Not saying you will or will not...but It would benefit you to take a long sit in one... The other red flag? Again if you don't like the plastic dash of The Honda Fit...I'd ask you to take a look and feel at a Prius Dash, I won't argue better or worse...but both are plastic. Bottom line..you cite Chronic Pain Issues...so Prius, Matrix, or Fit...or Corolla...(used Camry?)....Camry's get pretty good gas mileage for an ICE vehicle in the 4 cylinder configuration, and they are quiet and IMO very comfortable. ----But whatever you decide on...check the seat out thoroughly...