laying a floor over dirt

Has to be insulation plus concrete if thats in budget. You'll save some of the cost in reduced heating costs, and concrete can last most of a century, and if well done rather longer.

If you really cant justify any spend on insulation, its possible to use clean dry non-rottable garbage as functional basic insulation. Just let everyone nearby know youre taking clean palstics for recycling, and some will deliver it to your garden. Plastic film, bottles, clean food containers - nothing with food residues - and you've got some free insulation down there. Concrete blocks dotted (with the insulation between them) about can provide support for the concrete floor.

There are other neat tricks you can do when laying a floor...

NT

a suspended wood floor needs underfloor ventilation really. If that is a nono because of location, then go for DPM and concrete before you do anything..

Thats possible..

My inclination.

First get the level right - subtract the depths from finished and remove the soil.

Then whack some hardcore in if its at all unstable and oozy..

Do a sand blind on that and lay a thick DPM carrying it up at least as high as skirting..

Then lay some floor!Pour concrete with a mesh reinforcment, or none if its small.

Since this will be nice and dry, you can embed your floor joists straight in it as it sets..a few timbers tacked across will keep it all level.

If you leave the joists proud, you can run wires underneath or fit insulation between em.

I like the way you think ;-)