I don't know if it applies to the 2018, but there have been programming changes made for the suspension controller that could soften it a little. It'd be worth looking in to if you haven't already. Or the shocks could be defective and locked up- that's happened more than once. Once the dealer plugs in, they might be able to read info from the shocks and determine if there is a failure.
As far as the tires, out of the two sizes you mentioned:
305/45/22 would give you about .4" more sidewall, but a wider tread and likely heavier overall tire. It'd also be about .7" taller. That ~1/2" taller sidewall isn't enough to make any appreciable difference in ride quality based on the height factor alone. It's even less of a benefit when you factor in the other cons: Increased rotating mass, increased drag from the wider tread, taller tire skewing your speedometer and the taller and wider overall dimensions possibly causing clearance issues.
285/50/22 has a hair more sidewall than the 305/45 at .6" but is more than an inch taller overall. Still not enough increase in sidewall to feel and it'd skew your speedometer even more than the 305/45. Although it's the same width as stock, clearance is still an issue due to the height.
If you can stomach the "downgrade", 20s with 275/55 tires would be the most increase in sidewall while still maintaining a decent size of wheel. Otherwise, I'd focus more on the tires. If your Tahoe has the stock tires, there's a good chance they're the Bridgestone Dueler. These are widely known to be a stiff riding tire and have certainly earned their "Brickstone" nickname.
I recently switched from my stock 20s with Goodyear Eagle LS-2 to factory Tahoe take-off 22s with the Brickstones. What a huge drop in ride quality!
You're gonna pay for them, but it's been reported everywhere that Michelin makes some of the best riding and best functioning tires in the stock 20" and 22" sizes for these rigs.
