Reddit mentions of 0.8mm Ritza Tiger Thread - Waxed Polyester Braided Thread for Hand Sewing Leather (Mini Spool 25 Meters) …(Black (Mini Spool)) …

If you had fun and you're looking to dive further into it I'd suggest investing in the following:

• diamond awl like this
  
• diamond chisel(only really need the 2 prong and 5-6 prong) I use these
  
• good braided poly thread like this
  
• good needles John James
  
• Good skiving knife this ones a good starter
  
• Wing dividers I bought these
  
• Edge beveler Like this
  
• You'll also want a leather condition(neatsfoot oil is what I use) and a finisher(resolene, beeswax, snoseal, etc)
  
• Contact cement(Dap weldwood) helps keep things together before you sew them
  
• Dye if you want certain colors
  
  For ~$100 bucks investment and you've got most of the stuff you'll need to make good looking stuff, then you just need to buy leather. I highly recommend picking a project, watching some videos on it and then if you need a new tool for it thats when you buy it. My biggest mistake thus far is thinking I could bypass buying a hole punch, the quality using a punch is so much higher than trying to do it by hand.
  
  As for skills. Look up Saddle stitching, easy to learn and hard to master. With those chisels it makes it really easy to get a good looking product with saddle stitching. Wetforming leather, helps make those sheaths, holsters, etc pop out at you. I like watching Nigel Armitage and Ian Atkinson on youtube, informative and you pick up little tips here and there.
  
  You'll also need to learn to keep your knife sharp! So project 1 if you invest is make a strop and get some jewlers rouge to polish that edge to a razor!