The ultimate in comfort are the Tiger Den seats, which offer padded, moveable chairs and side tables. They are among located near the top of the lower level between the dugouts and behind home plate. Tigers Den seating is the most unique of any ballpark and are mostly in the shade (but they will cost you).
There are also cushioned seats available in the upper deck, often referred to as the club seats. The first five rows of sections 321-337 are seats that are wider and padded. They do not offer any other special perks, but they are definitely more comfortable than traditional seating.