I play a Mara, currently only Level 30 though. I didn't have any problem with managing abilities, I just dropped a few that I Didn't find useful.
As for a non-Quinn companion, I really don't know, I suppose you could use the droid if you still want healing, but the first time I used it(Technically it was on my Trooper, but I assume both droids are similar)he just kept running up to stuff, punching it, and dying.
I used Vette until I got Quinn, and that worked out fairly well, but a DPS companion won't really help much as a Mara, since you're already going to be doing monstrous damage.
EDIT: Also, are you F2P, preferred, or subbed? Even just one extra quickbar is great because you can put your speeder, self-heal, buff, quick travel, etc. on it to free up space on your main two