The Ryder is a nice plug, but I'd be slightly hesitant to recommend it. From personal experience I can say that 1 1/2" is manageable for someone just starting out, but the problem is that the Ryder is quite blunt and doesn't have much taper, which is where you'll get into trouble.
As an alternative I'd suggest another silicone plug from Tantus,
the Flirt. It has a long gentle taper, and is slightly narrower at its widest point at only 1 3/8"
I'd be inclined to avoid any plugs smaller than 1 1/4", because they'll be so easy to insert that you'll immediately want something bigger. There's no sense buying a finger-sized toy when you could just use your actual finger for the same purpose.