This is a good topic.
It's true you should use heel-to-toe. However, you may want to consider the type of shoes you're wearing as well. As for me, I wear flat shoes so when play the bass pedals- I use the following technique:
1.) I arch my foot to the left to play the Flat notes
2.) Then I press the white notes (natural keys) with my heel and begin to turn my feet towards the right to postion my toe for the next Flat key.
3.) As for practicing. I practice heel-to-toe on and off the bass pedals for about 20-30 minutes.
First, I go slow and hold each note for 2 seconds (to tell the brain - this is the correct position).
Then, I use a drum machine and practice the walking bass (slow, meduim, and fast).
4.) Finally, I practice walking the bass pedals chronmatically up and down - one octave.
_I hope this help. God Bless
-Al