I don't have a ton of experience in this area but I will offer my 0.02$.
First, I would recommend using the above link and doing a wet forming technique. This will produce a much prettier more professional look. It doesn't require special tools, just some wet leather formed around your knife. It will provide the best fit with the best look. I would wrap my pocket knife in saran wrap to keep any moisture out of my knife. Then wet the leather and stretch it over the knife. Just like in the tutorial. Of course you will have to wait till it dries then do some cutting and stitching to a back piece. This can be done pretty easily. Wet leather can really be formed to nearly any shape and when it dires it will keep that shape for the most part. That is one of the really cool things about leather work. Not only can you carve, tool, stitch, etc. but you can also shape and mold. This is your best option. IMO
If you still find that too difficult or dont want to do it for whatever reason you can always make a pouch for your knife. The pouch will not fit as nicely or look as professional, but it will hold your knife on your belt. Take two pieces of leather that are bigger than your knife and then just whip stitch around the edges like a small coin purse. you can even put a snap on it exactly like the coin purse if you want. Like this one minus the goofy cat picture. On the back side you can cut two slits for your belt to go through. Let me be clear, this will be a lot sloppier. There will be extra room in your pouch but your knife will probably not "rattle" around. It will work to hold your knife to your belt with practically the least effort involved (except if you just go to the store and buy one lol). All you need for this is 1) leather 2) knife for cutting leather 3)Some sort of lace to do your whip stitch 4) possibly a snap + snap setter. It might also be helpful to have a hole punch to put your whip stitches through, but you might be able to get by without this but it will be more difficult.
Obviously I cannot know exactly what you are expecting, but I hope this helps. Let me know if I can be of further assistance.
-Dr. Phil