I use and recommend Kelty Sleeping Bags.
Read reviews on Amazon and other forums. I would not go with the cheapest, but there is no need to spend a large amount of $$$.
Usually I would add 15-20 F to a bag for a normal person. A 28 F bag is more like 45 F and so on. We have a pair old Kelty Light Year 28 and my wife finds it to be comfortable down to about 38.
I like Down Sleeping Bags.
Used sleeping bags are a gamble because of smells that you might not be able to get rid of, I know.
Remember that it is not the air that will make you cold, but the ground. When frost is in the air a nice Air Sleeping Pad is a must. If you are hiking Air Pads are too big to carry and foam is the way to go. We no longer hike so I have a great Base Camp set up.
I wish my wife liked cold weather camping more, for I’m Oleg of the North People.😀
Good luck.