I hate that feeling, that if only you could keep them a little longer. It's like, "Wait, I'm not ready yet!" I considered taxidermy, but realized it would not keep my baby with me any longer. But it may help others. I just wanted a foot, or tip of her tail, like people used to carry a rabbits foot. But I decided against it.
As you have read, it is different for different people. If a piece of fur will help, or his favorite toy from before he was sick, just keep it. His eyes are so beautiful, it would be great to find two perfect marbles, one green and one blue, and carry them in your pocket for a while. I do have a necklace with a black cat on it, from an after Halloween sale. I have worn it when I lose a baby, or even if I have a day where I miss one really bad. My close friends know why I wear it, and it gives me a chance to grieve without having to talk about it too much. (Sometimes I just don't want to bring out the tears at work!) I'll wear it for Smudgie, when his time comes.
I like the idea of a photo album or memory book. I have a bunch of pictures of my daughter and her best friend at about 3 y/o, done on an 8x10 page as if to put in a scrapbook. But I framed it and hung it in her bedroom. Maybe you could do that for Smudge. They even sell acid free stickers, so you can add stickers to the page.
Prayers for his peacefulness, and for your wisdom in knowing when it is time. Hugs to you and the kids, and headbonks to little Smudge. If love could keep you alive, you would live forever baby.
I love you, Smudge!