Looking for a small puppy (Cushing)

Unfortunately my service animal is getting much older and I am looking for a small puppy that I can train to be my new emotional support animal.
I have PTSD, epilepsy, seizures and anxiety disorder.
I can't afford much when it comes to paying for a puppy because I'm on disability.
If anyone could help or maybe a good recommendation on where I can go to get one would be wonderful.
Thank you so much in advance.