I think any good quality multi vitamins are beneficial. I'm not a fan of the one-a-day you get at the grocery store.
Nioxin makes excellent vitamins for hair, skin and nails. I take those everyday.
I have extremely thick hairs, and I can feel bumpy and uneveness when i run a strand of my hair in between 2 fingers. They are "stubborn" and stand, making my whole hair look very much bloated... and very unmanageable....
It sounds to me that what you need are good moisturizers for your hair. Find professional quality moisturizing treatments. Vitamins will help your hair but I doubt that they will mke it softer.
As for the poofyness, styling products are the only thing that will help. Smoothing products and a flat iron (although the flat iron will contribute to dryness) will help take out the poof. You can use a heat protectant product to protect your hair from the heat of the flat iron.