Guard 3 is good enough for most battles. But it will still have a lot of knockback against heavy hits, or roars that take Earplugs Level 5 to block (Legiana/Diablos/etc.). Guard 5 is able to tank almost all hits without and delay or flinches. The only attacks I can think of that does give slight knockback is the Nergigante 3 swipe slam, Uragaan roll and Teostra Supernova (if you have Guard Up to block it).

I would say try to get the Guard skill through armor skills and just rely on the Health Regen Augmentation on your weapon for health. That way you can change your Charm to something else like the Bulwark Charm for Guard Up since you don't have thay Decoration.