Heel-and-toe is when you are applying the brakes. You have to be applying the brakes fairly hard to heel-and-toe properly, generally speaking for new cars. Personally, I only heel-and-toe when I'm on the highway going like 70 and then traffic comes up real fast and I have to slow down to sub-40 pretty quickly. Otherwise, heel-and-toe downshifting is just too aggressive for regular driving.

If heel-and-toe just doesn't make you comfortable (although it takes a ton of practice for it to become natural), try this...
let's say you wanna downshift and brake. Just blip the throttle and as soon as you blip, just step on the brakes while letting the clutch back out, engauging the lower gear. Or don't blip the throttle at all...personally, I always blip the throttle, but you can also just downshift and push the brakes while letting the clutch out slowly (clutch will brings rpm's up to proper speed without being jerky if you let clutch out real slow).

MrElussive
03 G35C 6MT

 

I've had no problems heal and toeing since day 1. The only that bugged me about the pedal layout was the clutch pedal which is rediculously too high. I already readjusted but the height and travel on the clutch. The brake and gas never needed it.

04' G35 Coupe(finally in the garage)
6-sp Diamond Graphite/Willow w/Premium