When sourcing pocket spring units, you must prioritize wire diameter (gauge), typically ranging from 1.6mm to 2.4mm, as this determines the firmness level. Additionally, the spring count (density) per square meter directly impacts support and durability. Ensure the springs are made of high-carbon steel with a tensile strength of 1600-1900 MPa to prevent sagging over time. The non-woven fabric pocket should have a weight of at least 60-80 gsm to ensure it does not tear during the mattress assembly process.