Another tiling job for pop

[cyclonebri1]

Hi chaps.
Youngest D just had a new extention and kitchen etc fitted. They now want the floor tiling.
Floor is old dining room extended into new kitchen and utility room. 35sq mts in total.
Old floor is quality tongued and grooved, extention is green chip, all pretty level.
Tiles are 300 x 300 porcelain.
The floors, both do bounce a little, so what would b the recomendation for pre tiling? I have used such as NoMorePly but it's expensive, 18mm ply would give step issues. Is there any point in going with 12mm ply screwed and glued tightly?????
Cost effective option please.
Also best adhesive option considering cost??
Cheers Chaps

 

[The Legend; Phil Hobson RIP]

Hi mate, I would not advise skimping on prep work. A few extra £s at this stage can save you loads of grief in the future. Brace the floor with extra noggins, and use 18mm exterior ply, you can use reducing trims for doorways etc. I swear by Mapei Keraquick with latex plus for wooden floors, a very good adhesive imo. Sorry I can't offer a cheaper alternative.