A 125 would provide you the ride you are looking for though as stated, you will need to change springs to suit your additional weight (though depending on your current skill level, you may just be able to get away with it for awhile).
However, there is another option. Several companies are producing 'between' bikes. Some are aftermarket while others are factory! I'm talking about the bikes in the range of 139, 144, 150 and 200. This provides the best of both worlds, the light and flickablity of the 125 and the grunt of the 250. Honestly, all are about the same (more or less) so it comes down to your wallet thickness and your favorite color.
And along those lines, you can always go bigger, but you can't get smaller. In otherwords, you can buy a 125 and later upgrade it to a 139 or 144 but you can never make a 250 into a 125. Just another thing to think about.