The next million times you’re alone, try this.
Touch a thumb to the index finger of the same hand, and breathe in. (You can do this with one hand or both. Either way is fine.)
Then touch thumb to middle finger, and breathe out.
Repeat a lot.
Now, if you want something harder, do an in-breath AND an out-breath on the index finger, and then move to the middle finger for the next in-out combo.
And if you really want to get exotic, you can work your other fingers into the act.