OK, here are a few things to consider:
What size hands do you have? It sounds as though you may have relatively small hands. If that is the case, many of the semi-autos out there may not fit you well. I have found that a gun that doesn't fit your hand well will exaggerate the recoil and make for an unpleasant shooting experience. I would suggest going to a fairly large gun shop and at the very least handling several models (if you can rent them that's even better but many places don't offer that). As far as which models to look for, bear in mind that guns with double-column magazines (the ammunition is stored in two rows staggered side-by-side in the magazine, these guns typically have a capacity of ten rounds or more) will usually have a fatter grip than guns with single column magazines (the ammunition is stored in a single vertical row inside the magazine, these guns usually have a capacity of nine rounds or fewer). Single-stack models in 9mm (just about the lightest recoiling caliber that meets your criteria) include the S&W M39, Beretta 951, certain variations of 1911 such as the Springfield Armory EMP, Sig P225, Sig P239, Walther P5, and Walther PPS (note some of these models are discontinued, but you may be able to find a used one). Models with double-column magazines that still fit small hands relatively well include the CZ-75 and Walther P99.
Action type should be considered as well. There are two basic action types for a semi-automatic: locked-breech short recoil and unlocked blowback. Locked-breech guns lock the barrel to the slide for a fraction of a second to prevent it from cycling until chamber pressures have dropped to a safe level. Unlocked blowbacks rely on slide mass and the weight of the recoil spring to retard the slide sufficiently. Because of this, most blowback guns are chambered for relatively small caliber such as .380, .32 ACP, .25 ACP, and .22LR. There are a few unlocked blowbacks in larger calibers like the Astra 400 and various models of Hi-Point, but these require either very stiff recoil springs or very large and heavy slides to work properly. A locked-breech design allows a significantly lighter recoil spring and slide to be used. Locked breech guns are typically softer shooting for a given caliber and have easier slides to work while blowbacks are usually quite accurate and reliable because of their simplicity.
All else held equal, the heavier a gun is, the less felt recoil you will have. Do not, however, get a gun so large and heavy that it does not fit your hands well.
Finally, to be be perfectly honest there is absolutely nothing wrong with a good revolver for self-defense. A medium-frame S&W revolver in either .38 Special such as a Model 10, 15, 64, or 67 or a .357 Magnum such as a Model 19, 13, 65, or 66 would be a very natural transition as you're already comfortable with S&W's manual of arms. Loaded with light .38 Special target ammunition like 148grn Wadcutters, you will have very light recoil but still a useful amount of power. As you become better able to handle recoil, you can step up to the stouter .38 Special +P ammunition and, depending on the model, .357 Magnum ammunition as you become comfortable to do so.
