Hi Tatyana,
We're so glad to hear our Leg Lifters helped your little one breathe better and get relief from his cold.
We strongly advise using SNOO and the lifters on flat ground without any additional props underneath. SNOO's incline w/ Leg Lifters is within the safety parameters set by the American Academy of Pediatrics creating a 2.5-degree incline.
If we can be of any additional assistance, please do not hesitate to contact us at customercare@happiestbaby.com.
Best,
Jess from the Happiest Baby Team