Ultimately you know what's best, so I can only say what I would do.  First, Gizmo has never been a tiny pup.  He's always been hearty, and we've never had any issues with sugar.
 
That said, I would do some research on vets.  I would find one in my area who has done a lot of neuters on toy breeds, and who will do the extra tests ahead of time.   
I know that it's a tough decision, but it could make him healthier and you all happier in the long run.  I have also read that it reduces the chances of some kinds of cancer, so it may even increase his life span. 
After checking into all of that, I would go with my heart.  I know what a tough decision it can be. 
 
 
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 The fullness of our heart is expressed in our eyes, in our touch, in what we write, in what we say, in the way we walk, the way we receive, the way we need. -Mother Teresa   (
 RIP Gizmo 3/9/07-8/18/12)
