Dear Stefanie,
Please, use the following code for Edit Form:
fd.spSaved(function(res) {
res.RedirectUrl = null;
});
And the following code allows you to save New Form, then redirect to Edit Form of the same item:
fd.spSaved(function(result) {
var listId = fd.spFormCtx.ListAttributes.Id;
var itemId = result.Id;
//replace "https://domain.sharepoint.com/sites/sitename/subsite" with path to your site
//PageType=6 means Edit Form
result.RedirectUrl =
"https://domain.sharepoint.com/sites/sitename/subsite/_layouts/15/listform.aspx?PageType=6&ListId="
+ listId + "&ID=" + itemId;
});