This is slightly tricky with trait bonuses stacking.
However, your Bred for War trait directly increases your CMB, which is one kind of bonus.
Then, if you have access to the particular religion (or DM fiat so it doesn't matter), you can try for Serpentine Squeeze, which gives you a trait bonus directly to your grapple checks, for both attack and defence. As written, this is not a +1 to CMB while Grappling, but a +1 to Grapple Checks, so these two traits should stack.
Perhaps less clear if it would work with the above, or even if legal because you're choosing to focus on Grapple checks, is the trait Heirloom Weapon. As written, there are no restrictions on how you can choose which combat maneuver you get a +2 bonus for, and although it states a trait bonus it also doesn't state specifically on what the bonus applies.
So, potentially, you would be looking at:
- A neat +4 bonus to Grapple checks
- and +1 to CMD versus Grapple.
Again, this is all reliant on how your DM will allow you to stack together your trait bonuses. But even in the worst case, you can drop Serpentine Squeeze and still keep hold of a reasonable +3 bonus to grapple checks.