in my cannon, I had a pet follow me around, is it ok to make a tulpa of him/her?

This depends entirely on your feelings. First of all, knowing your pet, how do you think it would have felt, knowing you made a tulpa of it? Was it sentient? If it wasn’t sentient, you should be fine, no question. If it was, you should consider whether it would feel replaced, or glad that you have someone to comfort you and remind you of it.