We probably can't answer Europe specific questions about where it is safe to camp in Western Europe. You'd be better off consulting with the authorities (police/hiking guides) in the areas you wish to camp in.

In backcountry areas here in the United States, person vs. person crime is rare.

Technically, you'll want a foam sleeping pad to insulate yourself from the ground. Your sleeping bag will only keep you warm on the top because you compress the insulation under your body when you sleep.