Shameless affiliate link here, but I've been a user of OwnX.com for quite a few years. All I do is automatically throw a certain amount each paycheck into this account and every time you get to 0.5 oz of gold or 20 oz of silver you can take delivery. They sell Gold, Silver, Platinum, and Palladium. Each time you make a purchase, they supposedly hold that silver for you in an insured vault until you're ready for delivery. Then you can pick from 1 oz coins or different size bars. You can also sell your holdings in your account as well.
It's insured through the mail and always requires a signature, so it won't just get dumped in your mailbox. I've dealt with their customer service a bit when FedEx kept missing me, and they're very helpful. They do charge a percentage of the metal for insurance and delivery and it fluctuates depending on the coins or bars you get. If you want to make a large purchase, there are better ways. But to slowly build up precious metal holdings over time without breaking your wallet or even thinking about it, OwnX has been a good choice for me and allowed me to build up a good collection over time.