Core muscles always help. My core is still quite weak after pregnancy, my boy is one, but I became very lazy and am now working on it. Staying aware that I am to tilt my pelvis slightly in, rather than throw it back as I have been.
I have recently purchased a back brace. It is to be worn for an hour or more each day. It certainly makes me aware of my posture the entire time I have it on, so I am guessing it "trains" you back into good posture. I will have to let you know how it goes. But so far so good.
For correcting forward neck. Now quite common with all the tech use, etc. There are several really good exercises on YouTube. Just look up "correcting forward neck".