Welcome to the forum and to backpacking.

Cheap, light and compressible don't go together.

You will need some basis for comparison before deciding to switch. My cheap Alpine 20 weighs 3 lb 4 oz including the stuff sack and a plastic bag. It's not very compressible, but since I have an external frame pack, it doesn't matter. I was given a Sierra Designs synthetic bag which is more compressible, but weighs the same and has the same temperature rating.

My dream bag is a Western Mountaineering Ultralite. It weighs 1 lb 13 oz.

When looking at down bags, it is good to look at the fill. 850 fill means that 1 oz of down expands to 850 cu in. 550 fill is only 550 cu inches. A higher number will be more expensive, but also lighter and more compressible.

You might be tempted to go to a 35 degree down bag. That works fine down to about 45 degrees for me. Then it gets a little cold. If you live in a warm climate, it might be a better option.

In my opinion, with a sleeping bag if you have something that works, keep using it until you can afford a really good one. Otherwise, if you keep backpacking, you may buy 2 or 3 bags before getting to the real good one. Keep in mind if you wait a year, the price will likely go up about 10%.

An alternative is to look for a good down bag from REI. Right now, they have 20% off the most expensive item you buy. You can get a really good down bag for about $329 before the discount. REI has a very liberal no questions asked lifetime return policy. If I were starting out, I might be tempted go that direction for about $260. But I'd probably keep dreaming about the Western Mountaineering bag.

If I wanted to take a chance, I'd get a bag from Zpacks. It only weighs 17 ounces and is $345 for the 20 degree bag.