I use #6 crosslock snaps (~150lb) with no swivel. I add a short piece of chafe tubing at the crimp crotch on my top shot, as that is always the weak link. I stopped using swivels. I don't think they are needed for most types of fishing I do.
P-line and Berkley make great crosslock snaps. There are much cheaper ones from China on eBay, but the quality is hit or miss.