Where to start?? I have 4 Snugpak sleeping bags in the loft (all man made insulation) Two Softie 6's (Kestrel) that zip together for warmer weather (comfort level 0C) , one Softie 12 (Osprey) which is for autumn temperatures (comfort -10C), and a Softie 18 (Eagle) which is for winter temperatures (comfort -20C).
Snugpak sleeping bags are British Army staples though they are quite bulky when packed but work when subjected to moisture.
I also have a Cumulus Mysterious Traveller 700, Down sleeping bag, comfort -10C but packs a lot smaller than the synthetic fill bags.
Finally a Western Mountaineering Ultralite down bag, (comfort -2C) but the lightest bag I have. This is my Go-To for lightweight, small pack size motorbike camping, really big bag so no getting wrapped up in it during the night. Disadvantage is - it's not cheap.
Buy the best you can afford, think about pack size and weight where you have space and carrying concerns, use a liner whenever possible to avoid the need to clean them too often, and store them unrolled as much as possible (I use IKEA Frakta blue zipper trunk bags and write the contents on the ends)
The next subject is sleeping mats...