Thank you for writing to us at the Community Tool Box with your question. In asking about a breastfeeding needs assessment, do you want your focus to be on the individual or the community? That is, for example, do you want to study the extent to which new mothers desire to breastfeed? Or rather the needs for supportive community structures around breastfeeding (e.g., provisions at work or in public accommodations)? Or something else? Sharpening the focus of and intent of your assessment is likely to help you find an appropriate measuring instrument.
While we are not familiar with needs assessments that specifically relate to breastfeeding, you might want to research and contact national or local organizations that support breastfeeding mothers. You can also find some information about needs assessment in general in Chapter 3 of the Tool Box. A good part of this may be relevant to your work.
We hope some of these thoughts may be helpful to you. Thanks again for writing, and all very best wishes for success in your work.