There are loads of SC apts in PM but they are private and not though an agent.
We have used them and they are lovely.
You get better facilitis, Washing machine , dish washer,fans, aircon, stereo ,dvd.
Just put a search in google for apts in P M and then get a flight.
There is a new complex being built with self catering apts, but no-one knows when it will be open The cordial valle apts.
First choice & Tompsons have it in there books.

First Choice feature some self catering apartments in Puerto Mogan called the cordial mogan valle