The best replacement for oo is ho.

The best alternatives to oo are rated as following:
★★★★★  ho
★★★★  procedural
★★  procedural programming
★★  n gauge
★★  ho scale
★  structured
★  oo
★  sdlc
★  soa
★  ew
  poe k
  short oo
  fp
  win tun

Your alternative for oo is not listed? Suggest!
Speaking about oo, one probably shouldn't forget about short u sound.

Other search terms related to oo and their ratings are:
★★★★★ short u sound
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Google Trends

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oo
ho
procedural