Here's a question - how much time have you spent with the game? Have you spent much time piloting with all of your skills maxed out? Cause you just take a lot less hits with a maxed out evasion skill. You gain a surprising amount of resilience as your skills gain levels.

If you haven't, then use the save editor from the Nexus (has been updated and does work), max all your skills, and see if you still think you need additional protection.

You can also almost always add more armor, because few if any mech loadouts come at max armor by default. Some mechs can see great improvements in survivability by losing a few or all of their jump jets, in exchange for more armor.

Then the final thing is, to never stop moving. If you slow down or stop to take shots, you're going to take more damage. The AI just has a harder time hitting you the faster you move. So unless you are WELL outside the enemy's engagement range (i.e. you are sniping with an ER-PPC), you never want to be stationary while in a fight.

I suggest using the save editor https://www.nexusmods.com/mechwarrior5mercenaries/mods/4 and maxing out your commander and AI pilots shielding and evasiveness. Set level cap to 10, and I think total XP to 76400 should be enough to max it out.
I don't have the numbers of what they actually do, but both at 10 are a significant increase in durability.

There's a damage reduction mod on nexus.

i know, but it doesn't work since the patch last week