I think if you have followed up with the person who last interviewed you as well as who would be your new boss, that is sufficient.
My last position I was interviewed by a couple of people including a couple from HR but the last was the President and who my direct supervisor would be. I sent him a quick note thanking him for his time and the interview and that ended up landing me the job.
I think you've probably done enough. Following up with HR might be getting to the pushy side of things. Just my opinion though.
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