Some of the links on this forum allow SMF, at no cost to you, to earn a small commission when you click through and make a purchase. Let me know if you have any questions about this.
A couple of things to help. Slow freezing reduces viability and most of us don't have blast freezers. If making the batch specifically for freezing, use more yeast as it will lose some viability and flatten the ball into a disk so it freezes faster.