Subfloor for decking

Hi all,

Im looking for a bit of advice, im a competent DIYer with a fair bit of project experience, but just looking for a bit of advice on a decking area im looking to build in ky garden.

This will be 4.5m x 3.5m against the house, and will be quite a heavy foot traffic area, with furniture on it also.

the advice im after is once ive framed the deck (not cement based), what type of subfloor should i use?
I plan to then lay tile backer boards and tile over it, but want to be sure that what im laying as the subfloor has the sufficient strength for its use.

I was inclined to look at a 18mm Plywood sheets, but also not 100% sold on its ability to hold the weight, the other alternative is treated T&G timber for the subfloor but obviously that is more expensive, the frame will be timber based also with 400mm noggins.

what would you recommend as the subfloor material/thickness that could handle furniture and some foot traffic (back entrance is accessed via it and is main door to the house)?

Appreciate your time in reading/replying.