Generally the onion bulbs are partially out of the ground, You don't need to dig nor pull to see them. When the tops are looking as you say, maybe thinking about falling over, go ahead and smash them over. Lay them down as in this picture.
Now leave them like that until the tops dry up. Then pull the onions and leave them lay on top of the ground for a while longer to dry well. If the weather is wet, bring them in the garage and spread them out to dry. They need to dry well for storage. When dry cut the tops off and store them.
Also be advised that if you want an onion to eat, you can pull one anytime. Have fun!
Gardening at 5000 feet elevation, zone 4/5 Northern Utah, Frost free from May 25 to September 8 +/-