If the smart balls are getting to hard to put in, I would say that you would want something smaller as the kegel balls are working well. Your muscles are getting tighter.
I have the Luna Beads Mini and after comparing specs they are smaller than the smartballs, so that might be a good way to go. The original Luna Beads are the same size.
As far as the pink and blue balls go, it really depends on how much you can handle. I love the fact that you can interchange the balls and experiment with different weights. The pink balls are the lightest, weighing 28 grams each and the blue balls are 37 grams each.
You could mix up the sizes using both pinks, then one pink and one blue, and then finally both blues.
Hope this helps.