I would not recommend going to 10 speed for a commuter. Everything will just be a bit more finicky and definitely wear more quickly. I would recommend a 9 speed if you must upgrade, and definitely no smaller than a 12 tooth small cog, 13 if you can find it, as I suspect your large chainring is 50-52 teeth. You don't need a 35 mph gear on a commuter. Better to space your cogs more closely together. If budget is at all a constraint stay with 7 speed, which is more than sufficient for commuting and much less expensive, as you already have compatible components.