Late to the party, but any nice black boots will fit the bill. Something like pic related (link below)
Occult themed jewelry is always a nice touch. Amazon links also below, two examples in pic. I personally have a St. Peter's cross necklace and cuff links, with pentacle/baphomet sigil rings.
The look I think you are going for is what's known as "corp goth." Black slacks, black boots/dress shoes, black vest, black tie/pocket square.
You can mix and match items from an outfit like that for casual as well. The nice thing about the goth look is that as long as you're wearing black, you'll mostly fit in at any goth club, even if it doesn't scream goth while on the street. I recommend eye-liner and eye shadow on top of a very light foundation, with black lipstick. If you have a beard, blend the foundation out before your beard line and do not use lipstick. Neatly trim all facial hair.
Mix and match textures, since you're primarily working with only one color. Other good options for outfits are anything you would traditionally think of as punk, but maxed out with black. Black jeans or slacks with a black denim or leather jacket, fishnets are usually good. Metallic studs, chains, pins, patches, all of it will work. Long sleeve tees, sweaters, anything works.
Find a style you like, go to thrift stores, search for deals on etsy, ebay and amazon. Personally I love amazon for more generic things, you don't need to go to alt or "goth stores" what you'll get there are overpriced and kitschy. Find some cheap black clothing, and DIY it into something you like.