Oh, I see. That's sad, then. But becoming the huge hippo is not actually a size increase, you can still cast Animal Growth on you. It will cost you another action, which might be a lot if you can't buff before the encounter. I hope you have a good scout. There is also another way to become big, and that is being lv4 Bloodrager with the abyssal bloodline. This way, you grow in size when you rage, no matter your creature type. You could use this to make the ooze grow bigger too, going for absurd amounts of cheese! So, instead of barbarian 1 and monk 5, you could go bloodrager 4 and oracle 1. You will have rage, immunity to fatigue and a size increase. There is no more table beyond 16d6 damage, but following the logic, I think it should rise to 24d6. That would go to a whooping 96d6 vital strike, dealing 576 absurds amount of damage in one punch! That would be the ultimate ooze!
Whoah, that's some cheese right there! I checked Inner Sea Magic to understand it, and it states that the guild bonus only rises effective caster level. Other class features aren't affected, so either the animal companion or the familiar won't scale any further. The full casting gish is interesting, though. The DD can be absurd with natural attacks and won't be a one trick pony like most cheese builds.