Dismounted Sipahi Lancers can be upgraded to Splint Mail which is better than Heavy Mail.

Just to recap here are the armor levels and their corresponding values:

Unarmored: +0
Padded/Leather: +4
Light Mail: +5
Heavy Mail: +6 or +7
Partial Plate/Splint Mail: +8
Full Plate/Heavy Splint: +9
Advanced Plate: +10
Early Renaissance Plate: +11

Note that certain units get +6 instead of +7 armor for heavy mail. They either use light brigandine or Mamluk-style armor.

The Mongols and Timurids use lamellar armor but I'm not sure how they fit in.