I have a sp101 357 in 3" barrel configuration. I had a pretty tough time finding a 3" holster you but you will find a lot of options for 2.25. I prefer full kydex holsters of iwb and owb. I was able to track down a Blade Tech kydex for my 3" IWB. I really like it. Leather hosters are fine, but i live in a climate that goes from 100 degrees and high humidity in the summer to 0 degree winters. This will be hard on your leather holster overtime and If your holster does not have a sweat gaurd for either inside or outside wasitband carry salts can damage your finish. With my leather holsters i do treat the outsides with a renovator to condition and water repel. I do not treat the inside. Galco would be fine, Fobus are inexpensive, Don Humme just keep searching. Good luck, keep in mind your owb holster will get dirty inside and out (like any holster) and kydex will be easier to clean and still have strong retention even w/o a thumb break
Check out Alabama Holster. They are awesome kydex holsters and offer great OWB options. I love their IWB holsters for revolvers. I would look into their "Offside" holster which is a tuckable holster meaning you are literally able to tuck your shirt in and all that is exposed is a small j clip. I rarely tuck in, but it is a great feature to have when you need to tuck. Now the grips may be noticeable on the sp101. I tuck my m&p340 in and it literally disappears which is amazing for thinner guys...5'9 150 lbs