I recommend a Bianchi Model 135 Suppression holster which can be found at the below link.

Model 135 Suppression™ Inside Waistband (IWB) Holster - The Safariland Group

That is probably one of the most comfortable holsters I have ever worn. I don't have one for my Shield, but I've carried a full size Glock 22/31 in it and you couldn't tell I was carrying a handgun. My second choice would be a Crossbreed Supertuck followed by Alien Gear.