Topping off doesn't hurt the battery.
If you had 95% battery and topped it off with 5% recharge, that 1/20th of a charge cycle.
Let it run down to 20% and recharge it, that's 80% of a charge cycle.
Also, above 80%, it does a slow charge. Below 80% it does a faster charge. I think slower charges are more gentle and produce less heat.
So each partial charge is only a partial charge cycle.
Apple - Batteries
I just plug it in whenever I can. I also leave it plugged in overnight so it charges, tops it off, then runs on A/C all night instead of on battery. Then it's full in the morning.
I also typically plug it in on the way home from work in the car.
They say about 400 charge cycles.
They do offer an Applecare extended warranty for about $70. You can add it any time before your 1 year warranty expires, and this extends it to 2 years. It covers the battery. So within 2 years, if it can't retain more than 50% of it's capacity, they'll replace the battery for you.
So Applecare pays for itself.
I'm going to get it at month 11 in to my first year if I think It will be necessary. By they I may be upgrading to a new phone or something so we'll see.