Insulation boards and/or self levelling compound?

[BB Kong]

Hi. Going to be tiling the downstairs of the house. Have a screeded concrete floor that looks pretty level (haven't checked it yet, but no majour bumps or dips). I was going to put down some self levelling before tiling, only because I thought it might make for an easier job and a better finish. However now we are thinking about some underfloor heating. My question is:

Is it necessary to use the self levelling compound and insulation boards, or just the insulation boards?

Thanks.