What about Abbott NeoSure? This is for premature baby, but always out of stock. You can call Abbott sales and order from them.
See my signature you will know how my BB gained weight. I have just switched to snow brand since 6-mth old cos of pooh pooh problem (before 3-5 days for 1 pooh pooh). After switched to snow brand, pooh pooh every day or every 2 days
My bb girl is also 8 months old, also she is a XS size bb (only 6.8kg). However, I think you should consult a doctor why your bb pool pool so many times per day. Previously, my bb also pooled 5-6 times a day, but it was normal because I breastfeed her. Since 6 months old, she only pools 1-2 times a day. If you feeds her with formula milk, she should not pool so many times.
Anyway, don't worry, take her to see a doctor. May I ask you that have you consult the nurse in health centre?
No matter which doctor you see, you're gonna hear him say " If only he or she is healthy, heavy or light isn't a problem!" I heard that a thousand time from doctor to doctor.