buying a tourist visa is no guarantee you'll be let in. If you are tagged as trying to stay long term on tourist entries, buying a tourist visa isn't going to change getting refused entry. You'll need a long term visa extension, not a tourist visa.
Never forget that immigration profiles, and stereotypes people. If you fit their profile they make it hard, or refuse entry, but with the DTV, which is a tourist visa, they can make you show an exit ticket, in keeping with rules, instead of overlooking them.
Be fully aware that for the extension you need to produce all the updated documents you used to originally get the DTV. By leaving and immediately returning you don't have to produce any documents other than your DTV printed out.
you are overthinking this. You will be fine. Also understand that buying a tourist visa does not guarantee you entry into Thailand, and actually brings more suspicion to you, as why would someone buy a 60 day visa when they get a free 60 day visa exempt entry. You've followed a pattern of being a tourist, not someone trying to live here long term on tourist entries. Don't worry. The immigration officer you talked to is correct.