My first thought is that since you're already close to the test, you don’t need to stress too much about buying additional mocks. Focus more on staying calm and well-rested because that will help more than anything else at this stage. At this point, new mocks probably won’t move the needle much since you’re already close to your goal.
As for your question about buying official mocks, if you have time and money to take 3 or 4 tests, then I would advice you to get the Official Tests 3 and 4. You can even repeat them once. There's no real need to buy all four remaining ones unless you've already used up the question pool. And this is mostly to keep you in the game and be mentally prepared before your final day.
In my case, the last six mocks I took were all official ones. I spaced them out by about five days so I could analyze my mistakes and reset mentally before the next attempt.