There are a million ways to make copression sacks, most of them are easy. Just copy something you like.
On the other hand, you might want to think twice about using a compression sack. Compressing insulation tends to compromise it and it will certainly take longer to fluff back up. Lots of wilderlings use the sleeping bag/quilt and other bulky items to fill out the empty spaces in the pack and don't even use stuff sacks, let alone compression sacks which can leave a lot of empty voids in the pack bag resulting in load shifting. Besides, a pack made with waterproof material protected by a rain cover is about all the protection a down bag needs. If you plan to take it swimming, line the entire pack with a trash bag.
Also, compression sacks are heavier than regular stuff sacks and always have a fiddle factor.