You want to look at ways to just flesh yourself out mechanically with the gestalt system. Druids get 4 skill points and a moderately interesting skill list, medium BAB, and 2 good saves. Adding a class with a good reflex save and either full BAB or more/better skills is a possibility here.
The other thing you want to think about is gestalting in a way that synergizes with your Druid class.Monk synergizes very well for a short while at least. A few levels works - getting evasion, wis to AC, flurry of blows and improved grapple is so good that many martial druids dip a level or two of monk, especially ones that plan on being grapplers. Beyond monk-2, though, the relative payoff wanes. The next two obvious choices are Psychic Warrior and an Incarnum class. Psywar gives more feats, and some really useful powers that you can't get otherwise -grip of iron is a great boost to your grappling, for example. It doesn't, however, boost your reflex save or BAB, though. Talashatora is a great feat that makes monk / psywar pretty sexy.
As a druid in wildshape, you're not likely to care so much about BAB either. Most druids opt for the claw-claw-bite routine rather than iterative attacks. So it's okay to stick with the medium BAB.
To that end, I strongly suggest the Totemist. It's an excellent class and synergizes VERY well with the druid. You can select soulmelds that further increase your AC and improve other abilities as well. You can gain even more natural attacks, boost your grapple into the stratosphere, gain what amounts to a constrict attack, or just go to town with skill bonuses. Plus, as mentioned earlier, you don't have to worry about stuff like magic items getting in the way of your wildshaping or chakra binds.
So, overall, I'd suggest you go monk 2 / totemist 18 // druid 20. Honestly, though, once you get to around totemist 6, you could probably start looking for another class if you're really *optimizing*.
If you can slap vow of poverty on top of that, you'll be able to kick even more butt.