One of the well known benefits of telecommuting is that you don't have to strap yourself into a work costume and trudge into the Real Office. You can pretty much roll out of bed and get to work naked if that's the kind of thing you want to do. I don't recommend this, mind you, because of the prevalence of webcams and windows and suchlike, but hey, I'm not here to judge.
Yes, you can be casual, but that doesn't give you a license to let yourself go, of course. No pajamas. I mean it. But do you need to make yourself uncomfortable? No, I don't think that either. Allow me to suggest real clothes that function like their more pajamaesque cognates.
Bathrobe? No.
Long sweater? Yes!
It's warm, comforting, and because it's long it can be helpful in managing the low-rise jeans/plumber issue that seems to arise these days.
Slippers? No.
Nice sandals? Sure, why not?
I like the idea of having a dedicated pair of house shoes, flip-flops or sandals to slip on, Mr. Rogers-style. I hate the idea of tracking dirt into my and home office, and I would prefer that people remove their shoes. But I understand that you might like to wear shoes to avoid seeming like a complete shlub.
Sweatpants? No.
Yoga pants? Maybe.
Here's the thing about yoga pants: elastic waist. It is a slippery slope from a forgiving waistline to sloth. I'd like to recommend that if you're going to wear work out clothes as clothing that this is only acceptable if you are actually going to or coming from the gym or other actual physical exertion.
I'm tying the belt on my long sweater and saying it over and over like a mantra: it's not a bathrobe.