Retrofitting insulation under attic floor

[rangy]

Hi all
I have an existing rectangular attic floor comprised of 5 inch t&g pine planks and been down approx.60 yrs and in very good u molested condition. . It measures approx 8mx4m.At each side, it has the usual space in the eaves and this is fully insulated but the main floor area was never insulated( probably not a thing back in 1963).
Each of the joists on either side have a cross batten between them, I assume to keep the joists straight and also to spread the load from above. Unfortunately this prohibits me sliding in any insulation from either side without taking them out which I'm loathe to do. I'm thinking of taking up one of the planks the full length of the attic as I don't want to take up more than necessary and then hoping to slide in mineral wool batts between the joists towards each of the cross braces.
Does this sound feasible or sensible or is there an easier way and a better material to use.? TIA

 

[freddiemercurystwin]

You wouldn't normally insulate a loft conversion floor.

 

[foxhole]

Should work or you could use loose lay insulation.