I doubt it's your driving style, unless you truly are making really short trips (like less than 3 blocks or so.) Basically, any 7 year old battery is suspect, and if it gives you trouble, replace it with a decent battery and the chances are very good your troubles will be over for another 5-6 years. If not, then you can start looking into more technical (and expensive) solutions like battery tenders, intelligent chargers, etc. But I seriously doubt you need that, so don't go there just yet.

In my experience, 95% of all "no-start" problems are either (1) an end-of-life battery, or (2) dirty/corroded connections. Address those issues before you even think about spending money anywhere else.

As far as what battery to buy, I've had good luck buying mid-upper range batteries at the auto parts stores. Never had one die early on me. (by early I mean < 5 years). In the grand scheme of things, $100 for a battery every 5 years is insignificant in the cost of vehicle ownership. Don't overthink it.