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.
i have no problems with CHA based character on dialogues/conversations. i wanted more options for other classes as main character. example, what if i'm barbarian instead? that should allow me to use STR checks in intimidation for example. As for monk or cleric, there's already some WIS based dialogue checks. everything based on CHA it makes dialogue/conversation useless for other classes.
i'm aware for some conversations you can use your companion which has higher checks for example but alot of conversations require the main character that initiate the dialogue.
