Don't get a back brace!
I've seen them advertised lately, and I'm actually stunned by how many people react positively to it. It shows a clear lack of understanding of what a posture problem is.
I'll go through the basics of why you (think you) want a back brace, and then why you shouldn't get one. If it makes sense, good. If it doesn't, that's perfectly fine, and you should seek a second opinion from your doctor, because posture is important enough that you should see one anyway.
The reason for a slouched back
A posture problem, such as slouched back (most likely the case here since the asker leads a sedentary lifestyle), is caused by the adaptive shortening and stiffness in the pectoral muscles. These muscles are responsible for pulling the shoulders forward, but when they're tight, they will constantly pull your shoulders forward, resulting in slouching.
On the flip side, you have muscles in your upper back that are meant to pull your shoulders down and back, which is the correct position for your shoulders. This is the common indicator of good upper back posture.
The reason your pectoral muscles get shortened and tight in the first place, is because of the forward posture we have when using a PC. Arms and shoulders forward, chest concaved.
How we generally repair posture
Knowing that tight pectorals are pulling your shoulders forward, we exercise our upper back. We strengthen these muscles so that they will become strong enough to pull our shoulders down and back. When they're sufficiently strong, they will do this, even while resting.
Additionally, we stretch the pectorals to counteract the tightness, and allow the muscle fibers to elongate enough to let our shoulders re-balance themselves.
What the back brace does and doesn't do
So what does a back brace do? It pulls your shoulders down and back, and bam! Now you have good posture!
Sadly, this is one of those cases of over-simplification.
Sure, while you're wearing it, it may very well do just that, but consider what happens when you take it off. Your natural posture will immediately show up again, and you've accomplished nothing. So what are you going to do? Wear it all the time?
The back brace may function as temporary pain relief if you're in pain, but all in all, it does absolutely nothing to fix the root problem.
What you do with this information is up to you. Personally, I have very little respect for those who advertise such braces because all it does it hold you. It does nothing to fix your problems. It is a cynical scheme to make money off of how little most people know about the human anatomy. Let's face it. If poor posture could be fixed by such braces, everyone would have perfect posture already.
So in the end, my advice is that you do NOT get a back brace, but rather stick to the tried and true. If what I said makes sense objectively, that's good. But if you feel like you need a second opinion, or even third, I encourage you to see a doctor. I'm confident that they will confirm what I've said. And besides, if you have posture problems, it is important enough to see a doctor anyway, because in the long term, it can cause a lot of pain and stress.
Note: This doesn't directly answer the question of recommending a good back brace, because I'm recommending NO back brace. Hopefully the answer still makes sense.