For me tofu, TVP, beans or lentils are great to add to any meal and i just switch it up based on what i have on hand and i like it. If you take extra firm tofu it will not break down much from anything.
Vegan Recipes
Collection of vegan recipes
Buy extra firm tofu, and press it to remove excess liquid and you'll be fine. I just put a cutting board down, then some paper towels under and on top of the tofu to absorb the liquid, and put another cutting board with some of my old textbooks on top. Leave it for 30 minutes or so. It might break apart in a crock pot, but it will still absorb the flavors and taste good.
I personally wouldn't do tofu in a crockpot. For simple "drop meals" I'd recommend an instant pot chana masala or lentil curry. Generally beans and lentils are going to come out better in stews, whereas tofu will come out better baked, like in this simple tofu curry or special occasion tofu tikka masala.
I'll assume you're referring to firm tofu. I think it depends on how long you're cooking the curry for. I don't know how tofu would do when cooked for long, but hopefully someone here does.
Tofu is already cooked so maybe you can put it in a crock pot the last 10-20 mins? That way it'll heat up and still absorb the surrounding flavours.
As for complete proteins, soy in general is a complete protein, so tempeh and edamame should count.
If you look up the contents, you can also mix and match different veg in order to get a complete protein. Chillis, curries, and stews are perfect for this because you can add anything with a bunch of spices, simmer, and bam - delicious.
Also, silken tofu is incredibly versatile. You can blend it to get a creamy sauce or to make a chocolate mousse. Highly recommend.
I've made tofu bourgignon many times with extra-firm tofu. I usually leave it all in the crockpot for up to two hours without it breaking down. It tastes amazing.