The best replacement for isofix is latch.

The best alternatives to isofix are rated as following:
★★★★★  latch
★★★★  seat belt
★★★★  non isofix
★★★  belted base
★★  surefix
★★  isofit
★★  easybase
★  familyfix
★  cabriofix
★  easyfix
★  isofast
  latch system

Your alternative for isofix is not listed? Suggest!
Speaking about isofix, one probably shouldn't forget about top tether.

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



Google Trends

Scale is based on the average worldwide traffic of isofix in all years. Click on graph for more.
isofix
latch
seat belt