The new silenced Reds and Blacks in the Corsair Strafe RGB MX Silent should be pretty quiet, too, and longer lasting than Matias switches (some have reported chatter developing after a relatively short period with these). But it pains me to recommend a Corsair, since they don't use a standard layout. If you're getting an MX board it's better to get one with a standard layout so you can swap the usually crappy stock keycaps with better ones.
Or wait until the silent MX switches start appearing on boards made by other more reputable companies like Ducky, Leopold, etc.
Quietest keyboard I ever used, though, was this:
I quieten my MX Clears with the trampoline and latex mods, but on most boards it require desoldering the switches to open them up.
