How to call attention to "I" without "I myself" or the pretentious "even I"?

I, too, have done this...

calls attention to it, while merely including yourself humbly in the long list of people who have done it.

I myself is fine grammatically, but two things. If it's conversational I have is too stilted. Also myself is more idiomatic at the end. Thus

I've done this once in a while myself.

I think you're right about "Even I".

"I myself" isn't bad grammar. You can use a reflexive pronoun that way as an intensifier, which is exactly what you want. But it's not exactly a common construction, especially in speech. I think it could come across as formal or outdated.

If you are describing why not to do X, then saying "even I" is not IMO pretentious because you aren't saying "even I, who would normally be above this behaviour" you're saying "even I, who you would expect to know better since I'm the one making this case".

Even I have to drive my own car

Pretentious. What, we should think you deserve a chauffeur?

Even I find myself boring sometimes

Not pretentious, people are expected to find themselves less boring than others do.

Another possible workaround if you're explaining everything anyway:

"X is a bad idea because ... Despite that, I have done this once in a while because ..."

This way if the second "..." is "I'm lazy" then you give more than a slight connotation of confessing, you come out and say it directly :-)

You could still intensify the "I" with "myself" or "even", but I think it's less necessary because you're creating a different kind of drama with "despite".