Laying hardwood floor over suspended floor joists; would any underlayment help?

[Neverfinished]

Hi, I'm about to begin lifting the original 'pine' planks flooring in my victorian terrace home. Then to lay American Ash (19Depth x 138mmWidth) planks, & I could just lay them again straight on the joists as originally. Being on the ground floor, there's the typical 3ft 6in ish 'crawl space' beneath, which has a well designed 'air-draught' thru; And at base just the original reasonably dry soil within brick foundations. See photo attached.

I've added 80mm of Celotex between the joists several years ago.

Original planks survived fairly well in the environment just described though had cupped, doubtless a long time ago, & had been 'face nailed'; I'm thinking I'd secret nailing this time thru groove in T & G might minimise cuping this time?

Would my new floor also benefit from 'shielding' from the elements, especially water vapour, down in that under-space? Perhaps I lay a 6mm plywood base ? &/or lay a Tyveck type breather membrane, on the joists ?

I've been a decorating, some carpentry, tradesman for years.

I'd much appreciate anybody's ideas / suggestions before I start. Thanks in anticipation !