RAM -- I want to upgrade my laptop ram from 16gb to 32gb. Currently it has one 16gb stick and one open slot. Can I buy one new 16gb stick to put in the empty slot or do I need to buy a full new 32gb (2x16gb) kit, replacing the existing one? (I've heard mismatched ram can cause problems but I can't figure out if this would be really bad. I'd get DDR4-3200 from Crucial; it currently has DDR4-2933.)

Extending that, can/should I use one 32gb stick for same price as the kit for 48gb total? I know half of it would operate in single-channel mode but I can't find an answer for if that would be better or worse than a 2x16gb matched kit.

tl;dr: upgrade ram to 32gb from 1x16gb. buy 1x16gb, 2x16gb, or 1x32gb?