Have you tried papaya enzyme tablets? They’re good for digestion and most rabbits go absolutely nuts for them. You may want to try these or other kinds of healthy treats to get him to move.
He may not be thrilled with your mild handling every day, but it’s not the worst thing – eventually, especially if you treat him after you do this, he will probably get used to it after quite some time.
The reason I say that another bunny might not be a bad idea is that your description of his attitude suggests to me that he’d be more interested in a bunny friend who might also be able to make him feel more comfortable and secure. How big is your enclosure? If there’s an x-pen attached then it should be all right for one other bun, they don’t need that much more room if properly bonded.
Since you’ve only had him for a few months, I’d give it a bit more time so that he adjusts fully to his home, and then look into potentially going on bunny speed dates to see if he might find a partner.
This isn’t a decision you have to make extremely quickly, but it may help to do this for the long run.