In addition to paddings, Suchet would initially trim the top of his hair to appear more balding (n later years his hair had thinned naturally), except in "The Mysterious Affair at Styles", which chronicles Poirot's first case in England where he's supposed to be considerably younger.
As of 2013, the entire Poirot canon written by Agatha Christie has been filmed for this series, with The Lemesurier Inheritance incorporated into Labours of Hercules, and Suchet giving a reading of the only stage play, Black Coffee for The Agatha Christie Theatre Company.
The trivia item below may give away important plot points.
When the series was canceled, David Suchet had grown so attached to the character, that he knew shooting his death scene would be emotionally painful. He asked that this scene be shot early on the schedule, so that the last scene should would still feature the character alive.