You have an excuse for a new rifle and that's never a bad thing. Though if you really aren't interested, then stay with the 300, I'd be looking at a bonded bullet like an A frame, heavy as I can get as well.
I built a 458 lott, I have degenerative disc disease, multiple herniated discs in my neck, the rest are bulging, severe arthritis. My back is now bad as well, rejected surgery by the insurance company so I haven't even had an MRI to see how bad my back is, doesn't matter at this point.
Wanted to build a 12lb 458 lott, ended up at 10 1/2lbs, it has a muzzle brake. 500gr federal trophy bonded bearclaws.
She is fun to shoot, it is an iron sight gun, that's it for me, shallow V rear, white dot up front. Fun though, no soreness, no bone bruising, even with a full bore heavy 500gr load, she's a hoot.
In ear custom hearing protection would be how I'd go now, I went generic fit $400 in ear and it's not great. But you'll hear better than normal, the custom fit will be as comfortable as can be, don't need to worry about your hearing.
Further, I think I could carry a years supply of those tiny batteries in the tiny little case I use for the hearing protection, so you don't really need to worry about batteries, they take up no space and were cheap.
So, if you want to go bigger on the caliber, it can be done and done comfortably, though I've never been one to mind lugging around a heavier gun either.
I know my dream gun for the hunt would be a double rifle, maybe a 470NE, dream gun for a dream hunt...
Though I'd note that I'd be bringing a call and calling the bear in once we got within reasonable distance, so a stopping style shot/frontal shot may be more likely. Would hope for very close, why the irons for me.
Just a dream for someone like me, I hope you make it out there, good luck.