Try using creative closures for sweater knits to achieve a high fashion look. Large snaps are an easy option. If the knit is loose, reinforce the area behind the snap with a circle of fabric which has been interfaced. This will prevent the snap from pulling on the fabric when it is opened and closed.
I sewed a decorative ebony button over the snap on my sweater knit jacket, which created an interesting design element and gave the sweater a finished look.
Try attaching buckles to a small piece of leather and then stitching it to the garment. Be sure to use a teflon foot when stitching the leather. For the closure in the illustration I chalked the X design onto the leather to follow as a stitching guideline.
Other options include making ties out of leather or cording, purchased toggle or buckle closures or a magnetic button.
Buttonholes may be used on fine or stable knits. Reinforce the area with tricot knit interfacing. Choose a stretch buttonhole from the buttonhole menu on your sewing machine . If your machine does not have a stretch buttonhole, try cording a regular buttonhole to prevent it from stretching. Buttonholes on sweater knits generally work out best if sewn with the lengthwise grain of the fabric, which has the least amount of stretch.
Zippers work very well with many sweater knits. Apply strips of lengthwise fusible knit interfacing to the cut edges of the garment to stabilise it before inserting the zipper. Apply double sided, water soluble Wonder Tape to the edges of the zipper to hold it in place while stitching. On the grey sweater top I serged the garment edges first, hemmed the lower edges and then applied an exposed zipper to finish the back of the garment.