Advice?

So I'm engaged, and have a three month old. I can tell my fiancée is starting to get bored with our sex life even though I try my best, I feel like it's always the same setting. We always do it on our bed. We try different positions and even on the living room couch but I feel like this weekend we should be spontaneous. I was thinking about doing it somewhere that's not at our home. Maybe car sex but don't know where. Any advice ladies?? I want to change it up a bit and catch him off guard.