Hi,
Well I can tell you that Post Finance do
not do safety deposit boxes. I know because I needed one recently and enquired about it!
In the end I went into UBS and asked about one. You
can have one if you are not an account holder but it costs quite a bit more than if you ARE an account holder.
In the end, I opened a savings account and then just paid a nominal annual fee for the safety deposit box.
Hope this helps

.