I agree with the cross-body bag idea. I do that and for nights out, I use a hand clutch and inside the purse, I attach my wallet which is this one which zips and locks shut for extra security.
If you are doing a cross-body bag, I’d suggest a strap material that is not easy to cut.
When I was in Barcelona with Topdeck, two people in our group were pick-pocketed. One person lost his passport and everything so be sure to lock up your valuables!