In addition to using Flex-Tastic here are 2 exercises Dina recommends to increase foot flexibility
Sit in a Kneeling position, tuck the toes under so that the toes are on the floor and the ball of foot are facing the wall directly behind you.
Put the full weight of your seat on your heels. You will stretch out the toes in this position and the ball of the foot.
You want to feel the burning sensation in the ball of foot and the toes. Hold for a minimum of 1 minute, work your way up to 3 minutes.
You may additionally get a stretch in your arches, depending on your level of flexibility.
Reverse it by first sitting on the heels so that the top of the foot is completely flat on the floor.
Try to keep your inner ankles and toes touching. If the bones in your feet are sensitive, place a neatly folded blanket under the tops of the feet.
No stretch here? Keep the knees together and separate the feet to the outer hips and sit between the feet,
slowly begin to walk the arms behind you lifting the tailbone slightly forward as you recline back.
You can take as far as you like until your back is completely flat on the floor behind you. Work your way up to 5 minutes daily.
