I would suggest you hit lots of backpacking equipment review sites. The thing about sleeping bags is there are hundreds of models. It's difficult to make a bad decision but it's easy to get a great bag that is inappropriate to your needs.
Here in Idaho, down rules and, brother, I take VERY good care of my down bags. I have not shopped for a synthetic bag in twenty years. I have no clue what's out there.
You may need a synthetic for lots of reasons but sleeping warm and comfortably is a complicated recipe of clothing, insulation, separation from the ground and, of course, ambient conditions. You can get by with a much lighter synth bag if you have an excellent pad and sleep wear and maybe a silk or polypro bag liner.
Good luck in your quest. Please think about returning to tell us what brand/model you purchased and how it has performed.