Specifically, what kind of shirt, pants hat should a man wear? Do any opinions advocate "downgrading" to less expensive/attractive clothing (in the same way that Halacha prohibits wearing of leather shoes)?
Your question implies that the reason for not wearing shoes on Tisha B'Av is a "downgrade" in the type of shoes one can wear on Tish'a B'Av as opposed to the type of shoes you may wear the rest of the Nine Days.
This is an incorrect assumption. The reason for the prohibition of wearing leather shoes on Tisha B'Av is because it is related to one of the five innuyim (afflictions) required on Tish'a B'av. One of these is ne'ilat hasandal - the prohibition of wearing shoes. O.C. mentions a custom to walk bare foot on Tisha B'Av. Few people, today, do this, and the prohibition applies to leather shoes, not rubber or plastic shoes.
So, in short, your comparison is based on the wrong premise, and there is no comparison. I am also unaware of any other clothing restrictions specific to Tisha B'Av that aren't already in effect during the rest of the 9 Days, such as not wearing freshly laundered clothes. Rama on O.C. 591:3 mentions that one should not wear "white" clothes on Tish'a B'av.