Some people say that a GSP will get along with a Ceylon, but I don't know this from personal experience. Several people seem to be able to keep a couple of GSPs in the same tank without problems, but I've only tried this with young ones and from what I've seen and read, it's kind of hit or miss - sometimes it works out, sometimes it doesn't.
For a while, I had a picasso trigger (a small one) in with my GSP, but I had to separate them after a few weeks because the trigger was bullying the GSP, so that combo is probably out. Right now I have two blue damsels and two green chromis in with her, and so far everything seems OK. At first, I think my GSP was put off by the activity of the smaller fish, but now she seems to pretty much ignore them and she goes about her daily business like normal. I of course can't say that this combo will work for you, as my GSP seems to be a very timid one, but it might give you a starting point.
I've wondered how a lionfish would get along with a GSP...I'm thinking that if the GSP is too big to look like food to the lionfish, the combo might work, but I've not tried it. (I don't really want a lionfish.) We keep puffers in with lionfish at work, and while you might think that the puffers would be wanting to take little bites of lionfish fin, we've not seen that at all.
Whatever you do, you're going to be gambling if you put any other fish in with your GSP, or most other puffers for that matter. Sometimes it works out, sometimes it doesn't. Things may go well for a while, but then one morning you look at your tank and all you see is a lone puffer swimming about with an innocent smile on her face and a very full, round, belly.
Whatever you decide to do, good luck! And let us know how it goes.
I kept a lawnmower blenny with two GSP's and they paid absolutely no attention to him. I took him out, (not enough algae to eat) and am going to be trying a snowflake moray with my puffs next.
75g 2 GSP's
37g FW community
10g Softies, Clownfish, Gobies and Shrimp
1.5g Betta
10g 1 Damsel, 1 Fairy Wrasse
65g LPS and Soft Coral Reef