My preference would be go with mattress topper first! I absolutely love microfill/fake feather toppers and they make a huge difference. It may only make so much difference to me because my back needs a VERY firm bed, but it hurts all the pointy bones to be on such a solid surface...
I absolutely love down duvets if I'm somewhere cold enough for one - I prefer them to any kind of hypoallergenic synthetic, but down is one of very few things to which I'm not allergic.
The pews never miss a sermon but that doesn't get them one step closer to Heaven.
But at least the pews never attend yoga!