I agree with this comment:
The present stance (championed by no less an authority than Pullum, I believe) is not to be precious where a technical ambiguity is 99% resolved by pragmatics, logic. Here, 'which is fully packed with commuters' addressing 'my office' would be ludicrous except in very strange circumstances that would demand being described. Your example is fine. // You are perfectly free to rephrase if that makes you happier.
-- Edwin Ashworth Jun 10, 2022 at 11:32
English is for communicating with people. Usually, people are going to be listening to try to understand what you are saying or reading to understand what you've written. They aren't usually parsing sentence structure or checking your grammar. That a sentence could be parsed to mean something different but nonsensical or improbable in a given context doesn't necessarily mean that it must be rephrased to be clear. The most obvious or sensible interpretation for the context is assumed, unless the sentence is very complex.
Sometimes ambiguity is used to make a joke (How does the "Dalai Lama walks into a pizza shop..." joke work?) or to create a headline that will make people want to read the article to learn more (How to eliminate ambiguity of "Sisters reunited after ten years in checkout line at Safeway."?), but for most everyday writing, precise placement of relative clauses isn't necessary.
If you intend to communicate the less obvious interpretation, then you would write in a way that forces it to be the only interpretation and that may take more than one sentence.
I take the bus regularly passing by my office, which is fully packed with commuters.
I take the bus regularly passing by my office. I work at the train station, so my office is fully packed with commuters.