I would check Amazon first to see if I get get one with free shipping in time for my travel. Depending on where us was travelling, that would determine what I used.
When I went to Europe, I made a simple pencil case like zipper case out on soft cotton that I put a binding along the top and snaps at the ends. I snapped the ends around my bra straps and tucked the cotton case into my bra. The zipper was at the top and I had access to my passport and traveller’s checks without worrying about getting robbed.