For multiple characters I use
Symbiotic Gauntlet 9.1 damage, 210hp, up to 9.1 damage more depending on hp
Sportsman’s Haute-Couture Kevlar 273hp, 204hp with shield depleted
Survivor’s Regrowth Serum 14 hp regen, and 7 hp regen after surviving 180 seconds
That is additional 677hp and 21hp regen, however Sportsman’s Hauge-Counture Kevlar works only for characters with shields, and you need to have hp to survive hit that depletes your shield. There is a legendary that will give you as much health without those limitations, but that would be pricy.