The best replacement for backless is high back booster.

The best alternatives to backless are rated as following:
★★★★★  high back booster
★★  high back booster seats
★  backed booster seats
★  high back boosters
★  high back
★  highback booster
  high back booster seat
  back bar stools
  back booster
  with back
  back booster seat
  highback booster seat

Your alternative for backless is not listed? Suggest!
Speaking about backless, one probably shouldn't forget about straps bra.

Other search terms related to backless and their ratings are:
★★★★★ straps bra
You have in mind a companion for backless and it is not yet here? Propose!



Google Trends

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backless
high back booster
high back booster seats