You could probably patent your invention without legal representation, but the real question is should you? On the surface, patent law in California seems quite simple, but any number of subtle or not-so-subtle mistakes could derail all of your efforts.
A reasonable solution is to work with a patent law attorney. Doing so relieves you of a huge amount of the "legwork" involved in acquiring a patent. It also has the added advantage of ensuring you have made no mistakes in your attempts to protect your invention.
By now you may be wondering just what kind of mistakes could upset your plans. As it happens, there are quite a few. For example, you may have failed to file for a provisional or nonprovisional patent application after selling your invention. This could mean that you will never be able to patent the invention.
In a similar example, say you do file for your patents, but you only complete the most minimal provisional patent application requirements. Failing to include a complete and detailed description of your invention provides you with very little, if any, protection. Further, if you use your invention publicly under an inadequate provisional patent application, it can also render your protection efforts largely worthless.
Getting back to your question, a better answer than the one provided earlier is that you likely cannot patent your invention "properly" without assistance from a patent law attorney. In addition to avoiding the mistakes mentioned in this post, a lawyer can help you conduct a thorough patent search and perform the proper internet research required to protect your invention fully.
Source: IP Watchdog, "The Top 5 Mistakes Inventors make with their Invention," Gene Quinn, accessed Sep. 08, 2017