Be aware, a few years ago a referendum was passed to create some controls for short term accommodations. These rules are currently being created by the city and should come any time now.
The goal is to reduce or eliminate rental arbitrage (renting an apartment to specifically re-rent it short term only more than 90 days per year).
Personal apartments will be permitted 90 days rental per year.
Other rules and bureaucracy will come along with it all, possible licensing, fees, inspections, etc...but we just don't know. The city and the Bern Welcome have not reached out to hosts to assist or consider our needs and wants.
Just one last caveat, the Bern market is currently in a large slump, day tourism has outstripped over-night stays by a long way. The market is already very competitive and satisfied, meaning there are enough apartments to fill the demand. It will not be a 'sure thing' simply to offer your place up for short term rent unless it's a few nights here and there.