You can custom make printed tshirst with your own designs or can ask them to design for you try IG @jessicamarie.sg You can also ask if they can make custom made clothes at reasonable price.
Shein has affordable ones. There’s also a website called toddleythoughts but it’s more towards tshirts/rompers.
Our second nature has some matching outfits. Or you could try Moley Apparels
PatPat is an app. There's babies + maternity + family matching clothes.