As a low budget gamer, I like to avoid spending money if I can. In your position, I'd want to keep using the 1200 Pro. That is, unless you have a specific reason why it won't work for you. Then I'd spend all my budget on the best headphones possible, leaving enough money aside for the mic. I believe you can get more use out of that 1200 Pro with better headphones.
That 1200 Pro looks to be rated for headphones up to 150 ohms. I usually don't like to push things hard so I'd look for lower impedance headphones. Open back is better in games, all other things being equal, but they leak sound in and out. Would that be a problem for you?
Gaming headsets tend to be tuned for gaming sound, which is great if that's all you care about. Getting good headphones results in still having great gaming sound but also sounding good with other things like music. It also depends on what you think is 'better'. What aspect of sound quality are you looking to improve? Sennheiser has a certain type of sound, if you mostly like what you have now you might want to consider just getting a better Sennheiser.