If you have trouble concentrating in salat, this is a chance to refocus on God and worship in the way that helps you connect best. Heck, it could even help if you've apt to rush through salat so that you can get to the other stuff on your mind. Rather than having those nagging thoughts about dunya at the back of your mind urging you to hurry up, you know that you have a set amount of time after the salat to dedicate to God. So, there's no sense in rushing the salat if you will be sitting afterwards in dhikr and dua.
Why not pick a dua and commit to making it after every prayer? Make it a part of your routine.