TDA7498MV heatsink fastening

Hi,

I'm designing a pcb for a TDA7498MV, which is a PowerSSO-36 package with exposed pad up.
Most of the designs I see are with glued heatsink or this kind of sketchy heatsink + fan https://ae01.alicdn.com/kf/HTB1EfqS...-Heatsink-40mm-Fan-For-3D-Printer-Cooling.jpg
Some designs uses screws to fasten the heatsink, like the Sure boards Trevor Marshall - Class D Audio Amplifier Design - TDA7498 Output filters

My design is made to be portable, so I suppose the most reliable approach is to fasten the heatsink with screws.
Now what is the best method to do it ? Is there special types of spacers to put between the pcb and the heatsink for this type of IC package ?
How to be sure the heatsink contact with the IC is even ?

Another constraint is to drill and thread the heatsink for the screws.

Any insight is welcome.

Thanks