If the best a 15th+ level caster can think to do to a sleeping party is polymorph your animal companion into a Behir- then you have nothing to fear from your DM.
Your party is casting 8th level spells and you sleep? You should be in your own demiplane by now...
Your DM is correct about the Gold Dragon not being your familiar any more. The rules for familiars allow for specific choices at specific levels. Anything outside of those choices is a houserule.
You remind me of a player in one of my campaigns. I was a newish DM then, and I really struggled with polymorph- trying to understand exactly what it did and did not do was driving me nuts. Skip's useless Rules of the Game did nothing to help- that just made the problem worse.
On our last session (we didn't quit because of this or anything- it was going to be the end in any case- we had a few people moving away), the player I mentioned, who was an 18th level Diviner, used Shapechange to become a Hydra. I mentioned casually that he would retain his Wizard BAB, and to account for that, which was true at the time (about 2 years ago). He threw a total hissy fit, just started screaming and yelling about how I was "nerfing" him and all this. Never mind that I could show him exactly where it said that in the PHB...
Not only that, he was singlehandedly taking on a huge horde of demons with a gated Marilith at the time. The Hydra Shapechange was just gravy.
Even giving him free entry into the Archmage PrC didn't stop his whining.
As I said before, your posts remind me of that guy. You might not really be that bad, I could be misinterpreting- but my advice to yuor DM based on what I've read from you so far is to dump you and not look back.