The legal side is, possession of cannabis is still illegal but up to 10grams it's supposedly no longer prosecuted, instead you merely risk being fined for 100CHF. However, I think I recently read that for instance ZH police still prosecutes for possesing less, Kanton Wallis apparently ignored
federal regulations at least not that long ago due to lacking authorisation of communal police to issue 100CHF fines.
Try Apotheke Langnau, the only one in CH that legally sells (sold?) THC products for cancer patients, including imported Dronabinol which is legally produced and sold in Germany. I thought I had read that the Apotheke had stopped that part of the business not too long ago, but the website (in german only)
is still up so maybe I'm wrong. At any rate they can probably provide reliable info particularly on legal issues.