I think a GoPro would topple it and a Phantom 1 really would struggle with a gimbal as well.
You've gone to the effort now, don't go and sell the quad for a newer one, stick with it.
Personally, I'd buy a cheap and cheerful second hand phone off eBay that is compatible.
I've got the trusty Phantom 4 standard here, had it for a while, along with my other DJI drones.
It's not been flown since September 2018 and I'm thinking of taking it out. All firmware is up to date, everything's charged etc.
But I was wondering if I should give it a gentle spin for 10...