I find that I can cover almost everything with T (target of target, not sure if this is the default mapping) and the F1-8 keys.

I have the boss targeted >95% of the time. The only person who requires spot healing with regularity is the MT, and that's accessed using T. To play cards on party members I use [Fx > Play > T] to target an ally, play the card, and return to the boss. There are very few times that I need to spot heal individuals other than the tank, so infrequently using Fx keys for that isn't too difficult. In the rare instance that my target is not targeting the boss I can generally use Tab to return to the boss.