Because your Mako is in such bad gear, you should gear her up better. You can either buy stuff on the GTN, from planet comm vendors if you have left over comms, and craft if you've been working on your crafting skill.
You've got two main defensive cooldowns, one which gives you 25% damage reduction and one which heals you, and in addition to these in solo PVE you've also got Heroic Moment. For medpacks, either buy some normal ones, or get some which heals both you and your companion (Biochem can craft them).
Use all of these defensive abilities in the middle of the fight when you need them.
You mentioned that Mako is in healing stance, but just to be sure, also check that all of her abilities are turned on (open the companion quickbar, make sure all abilities have the green box, if some abilities are not turned on, rightclick it to turn it on)
Also, almost every powerful boss in the game has some big attacks which you should interrupt, and it will make the fight a lot easier.
As level 35 PT DPS, you have your normal interrupt, your stun, and Grapple. Stuns and pulls work against most (all?) enemies in solo PVE. Look for what big casted or channeled abilities the enemy has, and interrupt them, don't waste your three interrupting abilities on anything else.
Another tactic is that in some fights, kiting and using LOS to your advantage works very well.
Lastly, have you tried tank spec? Might work well for you with Mako healing (that's how I leveled my Vanguard, PT mirror class). That'll also give you a fourth interrupt (Jet Charge).
I think the problem is that I've been skipping huge chunks of planet quests, because at lower levels I was about 4-5 levels ahead of the planets that I was on (see CrazedMike's Leveling guide).
Great advice if you want to waste time leveling to above where you're supposed to be and play the game on easy mode.
Everything in the game can be done at at least the level the game recommends, if you know the mechanics of the fight and are at least somewhat decently geared (both you and your companion).