Micro fiber not the larger fiber 8f you care about finish and seeing hairs in it.
I did microfiber and #4 bar 18 inch in center.
I put 3 inch rigid 60 PSI insulation under and I did regular 6 mil plastic under also.
2 inch insulation is fine I had 2000 sf leftover from a job.
No sweat from slab no cold from slab and the insulation and plastic reduce the friction on the underside of the slab so it won't have a tendency to Crack as it moves and hydrates.
I have 1600 sf 5 inch slab of 4000 PSI mix. I did low(er) slump and kept slab wet for a week to build strength.
I only cut one joint in it 3 years ago and don't have any cracks yet. ACI and every job I have ever done tells me not to do that but I rolled the dice and prepped the hell out of my subgrade.
For your question if you can find budget
Good solid subgrade, WELL compacted stone base min 4 inches, 2 inch rigid insulation, 6 mil plastic (taped best but a foot or two overlap fine), microfiber, and rebar at least 2 foot on center 18" better and a 4000 PSI mix. Lowest slump crew can handle. 2 to 3 inch slump
Insulation up the edges of the slab desireable also this is where most radiant cold comes from.
And last but not least a good finish crew to place. Don't "bless" the surface with a bunch of water, it thins and weakens the surface "cream".
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