One of the simplist ideas I know of is a rack for your tools. The spindle moves over the tool needed. Then down and clamps the tool. It then pulls the tool sideways out of the rack.
No moving parts except the normal machine movments unless you add a guard to keep the tools clean.
A more sophisticated version replaces the fixed rack with a round one that rotates, but the rest is basically the same idea.
Sorry no pictures of these