Which of these is grammatically better?

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To describe a situation that started when I fell ill and is ongoing (as I am still ill), is it better to say:

since I've been ill

Or:

since I fell ill?

I know I could say "since my falling ill" or "since the start of my illness" or "during the time I've been ill" (which is less specific), but I don't want to because they would make the sentence too clunky.

Which of my two preferred options do you think is best?! Thank you! :)

‘Fell ill’ sounds slightly more elegant, but they are both acceptable.
My God did I have trouble with autocorrect putting I’ll all the time there!

‘Since I fell ill’ is awfully 18th century! Is that the impression you want to give?

Lol, no, not ideally! :)

Thank you for the replies!

I wondered whether "since I've been ill" implies I'm no longer ill, but do you think that's not the case?

Depends a bit what it's for - Since I first became ill - would suit, say, a letter in which you're trying to be factually accurate, to a relative or an insurance company for instance. Since I fell ill, I think would be fine for a first person narrative piece of fiction.
Since I've been ill doesn't really work because the implication in 'have been' is that you're now better.

Ah we crossed...

Have been means you are still
Eg I’ve been here all night (I still am)

Yes … ‘Since I became ill’ is ongoing.

It’s ‘fell pregnant’ that gets me …

@MrsOatcake That’s why I’m unsure whether it’s grammatically correct to combine “have been” with “since”.

Yes, it’s fine. ‘Since I’ve been’ is correct.

Since I became unwell,

Indicates it is ongoing illness.

There’s an explanation of ‘since’ here:
blog.harwardcommunications.com/2017/09/21/how-to-use-since/amp/

Just don’t use “fell”. That’s an odd turn of phrase.

Since I became ill...

"Since I became ill..." or "Since I have been ill..."
are the better constructions. I wouldn't use "fell ill" as it is a bit too colloquial.

How about 'since the onset of my illness'?

Since becoming ill ...

@Clymene

Since becoming ill ...

This is the one I'd go for!

since the onset of my illness

This is not a person I want to hang out with. That ‘my’ makes this illness the only thing they want one to focus on. It’s not attractive. (Even if one feels all possible sympathy.)

Obvs if one is explaining a long absence from work …