Any experience with "emotional support animals"?

I suffer from pretty severe anxiety disorder as well as Post-Traumatic Stress Disorder. I see a psychiatrist regularly, have a number of prescribed medicines, and also have a regular therapist.

I used to have a dog - a lab mix I got from the pound - who would sit next to me on the couch or in bed when I was feeling anxiety. He made sure his body made contact with mine. He was so calm when you touched him - there was no muscle tension in his body at all, which was different from other dogs I have had. I also suffer terrible nightmares and he would wake me up if I was having a bad one. I slept so much better at night with him by my side.

He passed away, and I was hospitalized for a time. When I got out, I had to relocate to an apartment building that doesn't allow dogs. I understand that my state has a law that requires a landlord to allow a dog if you can get a note from a doctor or therapist that says you benefit from having an emotional support animal.

I'm not sure where to begin with this: how can I get a dog declared an "emotional support animal" when I haven't even adopted one yet? And if I adopt one, where do I keep him / her until I can get the official documentation?

One idea I thought of is to foster a dog, have my sister take care of him until I can get the documentation and clear it with my landlord. Then I can move the dog into the apartment.

Is this a workable solution, or should I save up the big bucks to get an honest-to-god PTSD service dog?

Thanks for anyone who has experience with emotional support animals or service dogs.