Learn English – “Have worn it” or “have been wearing it”

Yes, it is possible to use "ever since" with the present perfect. "Ever since" links two events, a cause event and something that is true from that point in time onward. This is actually ideal for the present perfect tense because one of the uses of the present perfect tense is to indicate that something which began in the past is still relevant in the present. An example of this use is your sentence:

"I always thought it was wrong, but ever since I read it, I've been more confused."

Using the present perfect with "ever since" shows that the speaker has been and is still confused by something which they read in the past.

With the past simple tense, as in your last sentence, it would be more appropriate to use "once" instead of "ever since". This is because "once" links a cause event with something that changed, but does not necessarily link to the present.

Once I did that, it stopped bothering me.

This sentence shows that the speaker was not bothered by "it" as soon as they did "that". It however gives not indication of whether this continues to be true in the present.

I saw your edit, if I understand right you meant to ask if it is possible to use "ever since" and present perfect without past simple, which would look something like:

"ever since" + present perfect + present

Ever since I have been pregnant I feel sick each morning.

The answer is no, this is not natural English. This structure may be encountered in informal English, but it is more natural to have the structure:

"ever since" + past simple + present perfect

Ever since I got pregnant I have felt sick each morning.

It's been a long time since I have read an interesting book.

"Why is it not present perfect + past simple? I understand the "it's been" part, since it's something that is still relevant or going on. But if I'm referring to a specific past event, why should present perfect even be considered?"

I was reading your statement, and began thinking. And although Hellion is correct when he said:

"in both of the sample sentences, you're not referring to a specific past event, but to a somewhat generic experience; you can say "It's been a long time since I have read an interesting book", but you shouldn't say "It's been a long time since I have read The Hobbit".

He forgot a detail.

What if the last time I had read an interesting book was indeed at a specific past event, for example, last month? Hence a completed action, my reading an interesting book, at a definite time in the past.

Could a person then say:

"It's been a long time since I read (simple past) an interesting book."

I believe the answer is yes. It is grammatically correct and makes sense.

Here is another example taken verbatim from "A Practical English Grammar" (A.J.Thomson A.V.Martinet):

"I've worked here since I left school"

Which means I have finished attending school (for whatever reason but the most plausible being I have graduated or taken my final year exams) and now I am working i.e. I am not a student any more but currently an employee.