Somewhat of an oxymoron - speaker stands for the floor for bookshelf speakers.

Stands are available at most audio outlets. The mark of good bookshelf speakers and stands are high weight. So, for a good speaker, you are talking 20+ pounds. For a high quality stand, high also. If you want to maximize the sound quality one should fill the stand with steel shot (in the old days it was lead shot). So together… you are talking about 40 or fifty pounds. So unless you are playing football 🏈 in your audio room there is no chance they are going to tip or be knocked off. I use vibrapods between my speaker and stands to decouple them from floor vibrations, and they are soft elastomer, so slipping is prohibited.

I sort of agree with ghdprentice. When I set up a pair of 'bookshelves' on stands I used some 24" high steel stands w/4 fillable posts and attached the speakers to the stands using a generous amount of Blue Tac. In order to counterbalance the speaker's weight I filled the stand's posts with steel shot. But, unlike ghdprentice, I only half filled them to keep the weight lower in the post and reduce it's 'tippibility'. BTW that Blue Tac really worked! It was hard to remove the speaker from the stand when you really wanted to. It did not damage the speaker in any way either. 

Education is awesome.  So,something I did not think of  -  while I was reviewing stands - how tall should the stands be?

Depends on the height of your speaker's tweeter (from the floor). Normally it will sound best when it is at ear level. Room and tweeter/speaker design might accommodate a slight deviation. For normal sized monitors we're usually talking about something between 24" and 28".