A simple CBC (Complete Blood Count) every month or so should tell your doctor how you are doing.
Since you have been diagnosed with MDS, you must have gone through a BMB (bone marrow biopsy.) A CBC is painless and very simple.
I certainly would not follow the advice of "if I started feeling ill."
There are lots out there like you and you should contact the AA/MDS International Foundation (
http://aamds.org/) for educational material and support. They should put you in touch with people that have been exactly where you are at this moment. Certainly folks in here will help you understand as much as we can.
By the way without a BMB it is most likely impossible to correctly diagnose MDS.