dnd 5e – How do we deal with my DM house rule about critical damage?

In the campaign I am playing in, our DM has established a house rule for critical damage. Then we do it

maximum damage for a dice game, roll the second game and add modifiers at the end

instead of the typical rule of twice the dice and modifiers at the end (PHB p. 196).

Example with an L1 Guide pin spell out:

  • regular critic = 4d6 + 4d6, average of 28
  • Critic of the house rule = 4 × 6 + 4d6, average of 38

It's great when you land a critic on the creature and it's fun and exciting. But, when a creature lands a critic with a special attack or a spell on one of us. You can easily eliminate one of us in one fell swoop. And much less damage of area of ​​effect! It is exciting and stressful. I really enjoy it, but I am the main healer. So, I regularly think: "Who will be next to blow up your clogs?" On one occasion I had the impression that the boss we were facing was going to have a final mortal movement before he died, he did. There was a massive explosion of energy and someone close was killed. Luckily I had run into a corner of the room at the same time and it was out of reach. The whole party was erased but the muggins.

What I am looking for is a way to thwart the critical damage against our group, if it exists.

I am do not looking for the obvious! We are already working to increase our HP groups, using temporary HP, reducing overall damage, increasing AC / save and having emergency supplies, spells and scrolls. We are also working together better, more tactically, doing things like expanding and not getting online when possible.

Is there any way to prevent a creature from causing critical damage in a natural 20? Or, is there a characteristic or class feat that specifically avoids critical damage?