I carry a lightweight fleece blanket with me... its a bonus no matter the weather because if it gets a bit warm, I open my sleeping bag and drape the blanket over me. If I'm the right temperature, I'll use the blanket as a pillow... and if its a bit nippy, I wrap the blanket around my head like a huge scarf type thing.
Having a setup in the garden is brilliant though, you can test out sleeping arrangements in different temperatures with little or no risk. My first time in a hammock was 200+ miles away in Dave Budd's wood... so if it all went pear-shaped, I wasn't going to be getting much sleep. Luckily I enjoyed every minute of it... and other than waking up about 3 inches off the ground (my lines stretched), everything went to plan. Did help that Dave lent me an undermat... surprising how cold the underneath of a hammock can get in the early hours.