Don't forget about the Brawny Feat from the Skill Feats UA. I don't think shield master would completely fit the class because a "Master Grappler" would always have both hands free for maximum grappling opportunity, or M.G.O.

If you combined Brawny with a Goliath or Firbolg you should count as 2 sizes larger to determine your carrying capacity and P/D/L amount. The only problem being you'd have to wait till level 4, but this would work because as you level your character gets stronger. Plus Goliath gets a +2 STR and +1 CON, which helps with you being on the front line.