Let me ask this question- if you were being attacked by a Great Dane or Mastiff would you rather have a 38sp or 357? Sure there are stories of Polar bears being taken out with 22 magnums but they had perfect shot placement.
We carry firearms because we do not know how or who will attack us. I have seen a BIG biker type shot with .38SP+P and the bullets stopped before an organs were reached. The body fat of that beer belly acted like a bullet proof vest and he acted like nothing happened. Most people consider the 38SP even in +P rating to be the starting point of what is just barely acceptable for self defense, ESPECIALLY out of a 2" barrel.
One needs to respect the knowledge and opinion of the one you are asking for information from. Many people think a 32 or 380 is enough gun and it is better than a sharp stick but you never know what you will run into out there. It is a gamble and I would rather have the odds in my favor. I would go with the 357. If you REALLY need it you will NOT notice any recoil and adrenaline will get you back on target fast enough. As to your choice the 158 grain semi-wadcutter hollow point (all lead with gas check as they can be driven faster than jacketed bullets of the same weight) in 357 would be a fine choice. That is also the most effective round for the 38SP in many NYPD studies.
Yes, you are correct, you can shoot .38's in a .357. But if you carry the .357 loaded with .38's you will be carring extra weight that will do you no good unless you have to hit the BG with the gun! The .357's are heavier than a .38 due to more steel in them to handle the presures.
That "extra weight" also absorbs a lot of recoil, helping to get the gun back on target more quickly
.38 + P is all I need. I shot a pig in the head w/ 158g JSP @ almost PBR from Colt Trooper w/ 6" Barrel. Clean through it. Too much for interior defence if concerned about over penitration the noise of the .357 will hurt in closed quarters. I carry snubby all day, everyday. It's heavy enough, I can't see carrying the extra weight.