The issue of independent decision making is enshrined in the Local Government Act which specifically refers to decisions of the council which can be delegated (or in some cases not delegated) to a "committee" and that a committee cannot be formed of just one councillor. Decisions can, in some cases, be delegated to a single officer but not a single councillor. In a nutshell, you cannot make a decision as a single councillor purportedly on behalf of your council.
There are of course a whole host of other issues relating to decision making, again enshrined in legislation regarding things like decisions being made in a public setting (unless you have resolved to exclude the public for certain specific and specified reasons), the requirement for declarations of interest, etc. etc. Mostly, these are included in standing orders but if not, legislation tends to apply regardless of what the standing orders actually state.
The Code of Conduct is an entirely different document based upon the Localism Act and is the document that governs things like treating others (including officers) with respect, declaring financial and other interests both on your Declaration of Financial Interests Form and in a meeting at which matters are discussed so that the public and everyone else knows that your vote (if permitted to make one under the Code) is potentially influenced by your connection with the subject matter.