I suffer from allergies so it has to be synthetic. I can't afford the silk ones so the options are either microfibre cover with hollowfibre filling (which is what I have at the moment) or with microfibre filling. I've never had one of those, are they better than hollowfibre? I tend to sweat a lot at nights but I'm also always cold so what would be best? They seem to be more expensive than the hollowfibre but are they worth it?