Help me save my party!

[Koujow]

Quick Background: We are currently playing the Dead Suns campaign and to say things have been difficult would be an understatement. The campaign already wiped the first party and recently, we escaped by the skin of our teeth against a difficult encounter and only after getting a full rest and heal were we able to overcome the encounter, against by the skin of our teeth. We completed book 4 of Dead Suns last night and we are now level 9. I need recommendations on what we can do to our party to help so that every fight isn't a near wipe.

Party: Minotaur Solarion, Vesk Soldier, Vesk Technomancer and a Kalo Mystic. The Solarion and Soldier are both primarily melee fighters, the Technomancer and Mystic are primarily skill monkeys (between the two of them, all skill checks are generally covered), the Technomancer does ranged damage while the Mystic has become somewhat of a heal bot. And as you can probably tell, we aren't exactly optimized.

We have some time before we reach the location of the next book, so we can craft items to help. Thoughts or suggestions on things to help prevent the inevitable wipe that will surely come?

[Pantshandshake]

Care to be a little more specific as to what keeps ending (or almost ending) your adventures?

[Koujow]

Damage. Even though the Solarion and Vesk have built themselves to be very tanky with a very high constitution and highest tier armor they could afford the last time we were in a civilized area, they keep taking huge amounts of damage. The Mystic has become a healbot only because they keep taking so much damage on the regular. 50+ damage a round some times! Even in random encounter fights!

[Pantshandshake]

Some initial thoughts, then:
Is your GM building encounters correctly? More importantly, are you in a game where the GM is actively trying to kill you?

Melee characters tend to take a lot of damage in this game, because they also tend to inflict more damage. If they haven't used feats, armor upgrades, or enhancements to get some DR and ER yet, they should try harder.

Tactically speaking, the non-melee team members might try using harrying/covering fire to swing the combat numbers a little, depending on what the melee damage output is vs the ranged damage.

More tactically speaking, are your melee people maneuvering to find any kind of cover from enemies, or are they standing in an open hallway getting shot? This can make a huge difference.

[Garretmander]

...That sounds a lot like your GM has way overadjusted encounters. My players rarely went into hit points until they adventured a little too long in the day. A CR 11 (which you should rarely run into at level 9) should put out, on average. <30 damage per hit, not 50.

Some context, minimizing spoilers, and also it went way off the rails so it shouldn't be spoilery anyway:
In the end of book six, my level 10 party of five players fought:
12 CR 7s
6 CR 9s
3 CR 10s
2 CR 11s
1 CR 13

In a running gunfight, most all at once with no 10 min rests for stamina, and just barely managed to come out on top, with three players in single digit hit point, one player having played whackamole with mystic cure 4, and another having received his first hit point damage the entire game.

[Elegos]

I'm gonna guess it was the 4th book boss fight, which is notorious for having its AC way too high due to a typo, confirmed by the author

[SuperBidi]

I agree with Garretmander and Partyhandshake: Your DM is making something out of the monsters. I'm currently finishing book 4 with a party of 4 (Solarian, Mystic, Mechanic and Operative) and I nearly never cast a cure spell.

Have your Soldier and Solarian taken Enhanced Resistance feat? It's a huge one, especially for survivability.
Mystics also have some defensive spells at high levels, giving DRs and resistances. It may also help.

Also, for your 2 casters, I strongly encourage them to carry a dozen of Spell Gems of the highest spell level they can cast. Without them, you spell starve during most dungeons.