It may be a subtle difference but the comma changes slightly the meaning:
"Almeno io sono così" means "there is at least me like that", it's not true that no one is like that.
"Almeno, io sono così" means "well, I'm like that", you're trying to justify your behaviour
I hope it helps and is not making things more complicated.
It does make sense, just only in very specific contexts.
For example, imagine a conversation between Alice and Bob, who are waiting on Charlie to arrive.
A: When do you think Charlie will get here?
B: I don't know, he's late even more often than I am.
A: Yes, but you're capable of being on time.
B: True. At least I'm that.
I spoke to a native Italian about this, because I was confused as well and I thought I detected a slightly harsh or sarcastic note about the translation. But he tells me there is nothing harsh about the sentence, its merely saying that you are that way - in agreement with what the person you were talking to said before you spoke. I am guessing we are going to run into things like this - where a direct translation doesn't necessarily make sense in your own language. Its going to be a bumpy ride!