I had the same problem with my 4 lb little one, I measured her and ordered this one on Amazon, it has worked great as long as it's pulled snug when put on! (especially for the price) Good luck!🙂

https://www.amazon.com/dp/B00J63SKFO/ref=cm_sw_r_fm_apa_i_Njk7Eb5PJHCPH