Mountain Hardwear - Lamina™ 30F/-1C

My preferred trip time is late September. I use a 30deg Lamina bag from Mountain Hardware with a Klymit Static Luxe pad. I generally sleep a little hot and prefer a cooler ambient. Weather will be your biggest obstacle: In 2021 I had an entire week of 80+ days and 60+ nights. I did not plan for that heat; slept on top of the bag the whole week. Last Sept I had a couple 25deg nights with high winds that were blowing in under the fly. I slept in my wools and on my belly with the face hole face-down and it was still a little cooler than I’d prefer with that wind cutting in. I’ll be adding a lightweight quilt to the kit for the future. (Everything was perfect for me tho on those 40ish deg nights!)

I use a Mountain Hardwear Lamina Spark bag for this weather when sleeping without a tent. These are relatively light and not too expensive.

My 11 year old 15 degree Mountain Hardware Synthetic mummy is as reliable as it gets, I've used it down to 22 degrees with a windchill in the teens and was comfortable. I trust it with my life. It's not even that heavy, right at 3lbs... only problem is that it's bulky. 12L stuff sack. I went with down for my hammock quilts, but if I have to sleep on the ground and worry about water intrusion or tent condensation, I'm using the MHW.

It's really a personal choice. I would suggest you try the MH sleeping bag. It's a free way to test a type of sleeping bag. Worst case, you buy another one later. I personally use down sleeping bags because they are lighter and compress better. But they are more expensive and take a lot longer to dry if it gets wet.