Charisma is a measure of force of personality, not just physical looks. However if you are having trouble with checks try the below.
1. Guidance (obviously) + 1d4 (concentration required)
2. Shapeshifter Boon Ring + Disguse self/disguise kit/mask of the shapeshifter + 1d4
3. Eagles' splendor + Advantage on Charisma checks (concentration required)
4. Ring of Geniality +1 to Persuasion and deception
Also Bliss Spores and the Nymph buff also help but they are only until long rest. This also won't help with vendor prices, since that is raw charisma, which you can only increase through Feats ASI, hags hair, or the Mirror of Loss.
Honestly, you should be fine with about 14 Charisma on your "face" character.
