TUTORIAL: Lenovo T440P M.2 SATA SSD Upgrade - YouTube
Lenovo ThinkPad T440 T440p T440s 256GB 22x42mm M.2 SATA III SSD | Dünya Grup
ThinkPad T440p SSD Upgrade with Transcend MTS400 256GB 2242 M.2 SSD – Mostly About Computers
Cha-m2b7-m256 256gb Ngff M.2 Ssd Module 256 Internal Solid State Drives With 256mb Cache For Thinkpad T440 Hot In Russia/brazil - Solid State Drives - AliExpress
Looks like m.2 2280 worked out just fine for t450s : r/thinkpad
ThinkPad T440p SSD Upgrade with Transcend MTS400 256GB 2242 M.2 SSD – Mostly About Computers