Changing coach interior Honrby mk1 coaches

[kingfisher9147]

Hi All, 

I am trying to turn a Hornby MK1 TSO coach into the Bar coach on the Gwili railway that I am modelling. I thought I was going to have a level floor but have to put up with Hornby plastic insert. What I want some help/advice on is what thickness of plastic card would be best to use to replace the plastic moulding of the TSO? the other problem I have with this build is the round circles that are on the coach floor where the coach bogies fit into on the floor as well.

Mike