You should be fine to use a moby. If you can try one out before buying go for it and if you find that it's a little short for you it's very easy to DIY one.
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Yup, you just may have to tie in back and tuck in the extra fabric. I was sz 18 when I first started using my moby when LO was a week old and either then or soon after I could still wrap it around to tie in front....then I washed it and no more!
Re: ? about Moby