Joist spacing

I'm in the process of fixing up a room to use as a workshop. It was once a verandah that has been enclosed at some stage. The floor is t&g, not sure what timber ( not hardwood.) I''ve cleaned up the boards and replaced a few rotted (borers?) ones.

I'm going to lay green tongue boards over top both for appearance and for a bit of extra strength. The guideines for green tongue say to that joist spacing should be 450mm, the spacing on my floor is 600mm. (90x50 hardwood joists).
Green tongue panel is 3600x900 and will be layed with long side parallel to joists. Will this joist spacing be OK?

The condition of the joists and bearers look OK. Bearer spacing is about 1700mm so I will be adding a couple of extra bearers (LVL 150x63) so that bearers will be at (about) 1000mm centres. Room size is 2400mm x 4000mm with bearers across the smaller dimension.

just use the 22mm thick particle board for 600mm spacings instead of the 19mm. each manufacturer will have different colour tongue.

Are you laying the particle board over the existing T&G or are you going directly onto the joists?

If it is over the T&G then I would think that the green tounge would be fine as it isn't spanning 600mm, it is using the T&G as the supporting structure.

use red tongue instead

The green tongue will be layed over the existing t&g.
I already had the green tongue otherwise I would have gotten red tongue as suggested.

No issue with it being laid on top of T&G as the T&G is already spaning the joists. Try to screw fix through the T&G into the joists

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I was planning to glue and nail, not screw because there will be no floor coverings, and I didn't want the fastenings to show.
I intend to apply a few coats of polyurethane as a finish, probably Wattyl 7008