The .357 Sig is an excellent choice in a defensive pistol. AS for what pistol to buy, as far as I am concerned the only choice is the Sig Sauer, model 229 or 239. I would also encourage you to purchase a .40 barrel. Why? .357 Sig ammo is very high and hard to locate at this time.
Premium grade ammo is selling for something in the neighborhood of $40.00 a box, you can still find .40 ammo at a reasonable price, so you won’t have to make it a “safe queen” because it is so expensive to shoot.
JMHO, but go with the recommended gun and extra barrel, you should be able to find one (used or factory rebuilt) for something in the neighborhood of $500, I recently seen them in a CDNN Catalog in this price range. The sky is the limit on a new one depending how you want it configured.
Some folks may debate the advice on a used Sig, but I have found them to very good guns, and never bought one that didn't function perfect!