when I looked into this for my loft I found the best method of
saving
the most headroom was to span steel beams with wood inserts across
the
longest length, and suspend wooden joist from them

I'm not sure I quite get this. Could you explain in more detail?


span a steel beam, say 8x5, either side above the ceiling/roof joists
below
bolt 6 x 2 joist inside the full length of the beams (you'll have to
drill the beam or buy one ready drilled) and attach joist hangers to it
then suspend the new floor joist from the hangers
the beauty of this method is you can set the floor height to anything
you like (within reason) by placing the joists between the ceiling/roof
joists below

Would a simple floating T&G floor be sufficient? Is there any need to
attach
the floor to the joists?



wouldn't a T&G floor would come apart if it's not secured ?