Hi Maria,
For 1-1 material link, you can use Vendor material number.
1. Enter vendor material number in PIR.
2. That vendor number field will be captured in PO via PIR. Under 'Material data' tab item level.
3. This vendor no. field can be reflected in MIGO-MB1A via some development.
4. To check for stock or to search the vendor material number. This field is available in F4 search items and can be viewed in many reports like ME1M.
2nd option is to go for manufacture part no. but to use it you need to activate it in custimization.
My suggestion is to go for vendor material number.
Kindly let me know if any query.