Two things:
1) in racing, double clutching doesn't exist! Just takes up more time and who cares about syncs, the gear box is replaced regularly.
2) the best trick to find your rpm at any speed is to get a feel of the relative ratio of gears. The beauty if this is that the ratio is constant throughout all speeds; for instance:
Say you were at 60 km/h as previous example, and after downshifting, you found the increase in revs is 1800 rpm (as previous example) then when you down shift from third to second, always add about 1800 rpm!!! Your problem is solved! This is how it is done by the pros (me being trained by them)

As for heel-toe trick, try this for big feet: put your 'wide' foot half on brake, half on fuel (as if you are trying to fit your foot between the two pedals), so instead of heel and toe, you wigle your foot left, to increase braking, right to blip fuel. Works magic in my case and in case of emergency, i press hard ON BOTH but with clutch so all is safe!