What y’all recommend for Spring - Fall (maybe down to 30 or dip to 20s
Snugpak Jungle Blanket works great! Light, warm, small.I use Snugpak quilts when I hammock camp but I haven’t been in 20-30 deg weather. @BurnedOutGeek probably has a wealth of info on this topic. MacIntyre or something like that makes them too
is this in addition to a sleeping bag?
How far are you walking away from the car/truck?
Wool blanket folded so you have some under and some over, number of folds depend on the temp and any other layers you have available.
I use a Jarbridge underquilt from https://www.arrowhead-equipment.com/store/c3/KAQ_Synthetic_Quilts.html and a down sleeping bag opened up like a quilt for the top. in the summer I go with a fleece line top but still use the same underquilt. These folks also get great reviews and are here in NC http://wildernesslogics.com/
Talk to the folks at the Hammock Hnager Forum for great ideas https://www.hammockforums.net/forum/forum.php
I think the real money is in the under quilt to spend for the best sleeping, considering frozen butt is an issue with hammock.
If it's really cold find the foil covered bubble wrap. Use it in place of a sleeping pad. If it's cold enough to use this I am inside my sleeping bag so I'm not laying directly on it. I use the insulating wrap that comes in tractor trailers. But you can find it as a windshield protector too. Or this.
https://www.homedepot.com/p/Reach-Barrier-4-ft-x-25-ft-Air-Double-Reflective-Polyethylene-Insulation-Roll-DD48025/204476656?cm_mmc=Shopping|THD|G|0|G-Pro-PLA-D22-MaterialsSupply|&gclid=EAIaIQobChMI5fTS6dKa2QIVG7jACh1O4QAcEAQYBCABEgIqyvD_BwE&gclsrc=aw.ds&dclid=CPDuwozTmtkCFc7HwAodkZYEbw