According to p. 187 of the PHB, you can use your Performance skill to maintain a wealthy lifestyle during downtime, if you have proficiency in it.
Does having the Jack of All Trades feature count?
For reference, the PHB states on p. 57 that
[...] you can add half your proficiency bonus [...] to any ability check [...]
It states "add half your proficiency" rather than "are half proficient," however that may be because it applies to things that you cannot be proficient in, e.g. initiative.