URGENT help against SIDS, reflux baby

I don't get much sleep out of worry, as because my LO is 9 week old and as she has reflux we have to have her cot tilted,  but now she kicks and wriggles she ends up laying at the bottom of cot despite us putting her feet at the bottom and ticking in tightly. it's so scary to think she may suffocate one day. We stopped using tucked in sheets as she would end up underneath, we've tried a band of tight sheet over just her tummy almost tying her down but still wriggles down, she's Been in a sleeping bag for the last few weeks to stop the risk of her being under the covers but she still ends up laying horizontally.can anyone advise please.