Gardening vegetarians and vegans: what sort of fertilizer do you use?

I’m new to gardening and I’m using liquid seaweed for my tomatoes.

People at the gardening centers have been telling me I won’t get awesome tomatoes without using blood meal/bone meal.

Have you used seaweed? What do you use?
I would really love to be composting, but I live in a one-room apartment that’s smaller than my childhood bedroom. I’m trying to garden on my huge, south-facing windowsill. We’ll see how it goes.

I’m Vegan. I grow cabbages, peas, carrots, corn, tomatoes and butternut squash and I use NO fertillizer what so ever.