Here are a few to begin with. I'm not sure how you define 'different' mates - is that the key move only?
Mate in 1, White to move:
Mate in 1, Black to move:
Mate in 2, White to move:
Mate in 2, Black to move:
In this position that I composed long ago (this position is legal), every move is completely forced and it is checkmate in
!8 moves (15 ply):
1. Qxc7+ Qxc7+ 2. Qxc7+ Qxc7+ 3. Qxc7+ Qxc7+ 4. Bxc7+ Kb7+ 5. Bb8+ Qxe7+ 6. Qxe7+ Qxe7+ 7. Qxe7+ Qxe7+ 8. Rxe7#
EDIT: Actually, seeing the "only one line" requirement, here is a 16 that is a slight modification of a position made by Bernd Schwarzkopf and Karl Scherer (Urdruck) im Feensnach 1980 on page 13. A PDF can be found here.
! FEN: 1KN4r/r7/k7/pr2R3/5b2/8/8/8 w KQkq - 0 9 (Picture Please!)
! 1. Qxa7+ Qxa7+ 2. Rxa7+ Qxa7+ 3. Rxa7+ Qxa7+ 4. Rxa7+ Qxa7+ 5. ...