Hmm, for a 1.2m cot with a 10cm mattress, the main thing to check is that the bed guard's height is proportionate, with such a low mattress, you don't need a very tall rail, but you want one that still slots in securely without gaps at the bottom. AiHome is one brand that comes up quite a bit locally; their rails are designed to fit Singapore and Malaysian bed sizes rather than the longer European 2.0m standard, so the fit tends to be more practical for our local setups. Some options work better on lower mattresses than others though, so it's worth confirming the minimum mattress depth requirement before buying. Overall I'd say measure twice and check the product specs carefully, the fit really depends on your specific cot frame and mattress combo.