I'll try to elucidate for you: planked wooden floors not only move with loading (of the joists, mores so if the boards are square edge not T&G) but they also swell and shrink with changes in atmospheric humidity as the seasons change. The boards themselves can also be uneven. All this makes planked timber an unsuitable sub floor for use directly beneath any type of parquet, which requires a flat stable sub-floor beneath it with minimal joints, and is why you rarely find parquet above the ground floor on historical buildings unless it was being laid onto concrete or stone flags (often with mortar on top). However, you can produce a similar flat, highly stable sub-floor by either fixing 6mm cement fibre board on top of your planked sub-floor, or possibly by nailing 6mm plywood (at 100mm centres) or screwing it (at 150mm centres / 100mm centres nearest the board edges). BTW that 6mm figure only applies if your planked floor is flat - if it isn't your sheet material will need to be thicker - 12mm or even 18mm.
You say you are on a limited budget, but have you factored in the necessary tools (or hire thereof) to install and sand the floor? All the recovered parquet I have dealt with has come in slightly randomly sizes as well as some of it having bits of bitumen still attached. So it takes a table saw to sort it out. And after it has been laid you'll need a floor sander to flatten the floor. Even if you are laying the modern plywood-backed "recovered" parquet sections you still need a flat, stable sub-floor to work from
And on the subject of cost, have you factored in the high cost if parquet adhesive?
Sorry to be a naysayer, but good results always require good preparation - and you seem to be prepared to scuttle your boat for lack of adequate sub-flooring prep
