What I'm playing with is shrinking a linear supply to as small as I can get it.
For the heat transfer paste I use the newer silver bareing artic freeze, it is by far better than the white silicon paste.
CAREFUL, you need to avoid the BIG mistakes that Pyramid and other low-cost linear power supplies made -- along that line of thinking. Later versions of those power supplies had to add a fan, to increase circulation, to address the design mistake -- and failure rates due to thermal issues.
You need a properly sized heat sink to transfer (radiate) the waste heat generated by the pass transistors.You can not by-pass basic physics ... laws of thermodynamics ... out of desired design convinence.
Aavid (major heat sink mfg.) has many resources and specifications for the designer ... to select the proper heat sink.
I have been migrating from traditional Mica insulators/grease to Silicon-Fiberglass ThermoPads (by NTE and others)
available from major electronics distributors (Allied, Newark, Mouser, DigiKey, Future).
NTE's THERMO-PADS do away with the old fashioned mica wafer and conductive grease method of mounting power semiconductors.
These thermally conductive insulators offer low heat transfer resistance while still providing high electrical isolation between the parts of the assembly.
The elastomeric material combines the electrical isolation of rigid insulators with the ability to conform to rough surfaces and reduce contact resistance in much the same manner as thermal greases.
Proper selection and use of these THERMO-PADS results in a securely-mounted power semiconductor and minimum resistance to the heat transfer between it and the heat sink.