My girlfriend and I are going camping in Europe this summer and are starting off in Spain. We have [this tent][1], and are looking into sleeping bags. We have also been keeping an eye on the weather in Spain at night time and are wondering whether a sleeping bag is actually needed? We don't really want to spend a load of money on a sleeping bag if we're just going to melt in them. 

Maybe we just don't know enough about the right sleeping bags? 
We were thinking maybe just getting sleeping mats and a small blanket. 

Has anyone got any experience that could help us decide what to do?