I know I have a lot of friends among needlewomen who always sew on buttons in a single puncture. The disadvantage of this method is wasteful use of threads. There's a quick and easy way out.
So, put 4 threads together, needle them. You can take a wide eye needle.

... together it's already 8 threads that provide secure attachment.

No knots. Pierce in the right place and pull the thread, leaving a long "tail"...

...and pick a button.

Tie the thread.

I make a double "girly" knot. None button has teared off yet. You can experiment with it.

Cut off the threads.

This is how the result looks from the inside. And the inside is a face of the product, actually. Enjoy the craft! :)