Sludge is poor maintenance interval. Varnish is usually textbook religious scheduled OE/dealer recommended intervals.
Vary the 5w30, 10w30, 0w40 full synthetic oil brands/grades. And, keep the oil/filter change interval every 5000 miles or less. Engine will clean up all by itself with current spec oils. Go thicker if there is oil consumption. Follow the HTHS ladder. You will find a grade/brand that might reduce consumption, especially if excessive now. If not excessive, then its normal!
Use an oversized filter. The PH4967 thimble can be upsized to the 4386, 3614, and 3600 filters.
Replace the PCV valve, plugs, thermostat, coolant, cap, transmission fluid, PSF, belt... normal maintenance to get it running good, efficient, and clean. Most of my o2 sensors failed at around that mileage on my Toyotas. Run a quality FI cleaner.
Add a can of BG MOA 110. Its discontinued but still available. Was replaced with lspi MOA 115 and greenie MOA PE06. Other cheap and easy to use cleaners would be a pint of solvent from MarvelMysteryoil or Rislone, detergents from STP Synthetic oil treatment(gold botle), or maybe some help from the ester in Lubegard Biotech. Honestly, I don't see the need to clean it if you start using synthetic oil and a sane interval, and keep it full always. Check that dipstick often. My 1.8's never developed the known oil consumption issues but ran 5k synthetic intervals since new.
Being a Toyota, other than the current tuneup, don't see it needing much, other than timely maintenance and full oil levels. Don't see the need for overpriced additives or oils. Local autopart stores and walmart have fluids/filters and looking for rebates, sales, clearance fluids... will keep it running for a long time. If you're ok with 3k interval, don't even need synthetic oil either.