Having done something so often, that it's all routine

I would like an expression that emphasizes that you've done something lots of times, that it's just routine to you. I thought

"I've done it so many times, I can do it in my sleep"

might work, but I'm curious if there's any better alternatives.

A person who has completed successfully a task many times in their past would probably say: it's (like) second nature to me.

A habit or mode of behavior so long practiced that it seems innate, as in: Driving in heavy traffic is second nature to Chris.

This expression is a shortened form of an ancient proverb “Custom (or usage) is a second nature”, first recorded in 1390. It alludes to the fact that very frequently repeating something makes it seem completely natural or inborn.
_{The American Heritage® Dictionary of Idioms}

You could use with one's eyes closed which means:

to do something very easily: 'I've filled in this form so many times, I can do it with my eyes closed.'

[Cambridge Dictionary of American Idioms]

"I can do it in my sleep" or "I can do it with my eyes closed" could also mean the task or action you are doing is very easy.

I've done it so many times, I can do it blindfolded, [one hand tied behind my back], [hopping on one foot]

do something blindfolded

If you can do something blindfolded, you can do it very well or easily because you have done it many times before. She could find that house blindfolded.

Merriam-Webster Learner's Dictionary

Also, do something standing on one's head

could do something standing on your head (informal)

if you could do something standing on your head, you can do it very easily, usually because you have done it many times before

I've done this job for so long I could do it standing on my head.

Cambridge Idioms Dictionary