There are some nice, affordable fully regulated drivers in ∅20+mm formats, at least for the tinkerers who aren't after extreme outputs. Drivers like the LD-29, H1-A and H2-C are among my favourites.
Fixing the SK98 may take some work, depending on whatever pill you get. If you buy a genuine UltraFire SK98 (@ FastTech, homepage link here) you'll get a hollowish pill with 2mm shelf and ≈11.1mm inner hole, not too bad for stock power output. Take a look here if you will.
By the way, seems to me SK98s do feature quite good heat dissipation, am I right? In theory my SK98 burns up to ≈25 - 26W (XHP50 at ≈3.6A) on high but it doesn't exactly gets hot super-fast. 
Cheers :-)