It was a more difficult life than he was used to, so he had to work hard to support the family.

这不是省略动词，这是个后置定语从句省略了life
正常的语序是than （the life） He was used to 比他以前所习惯的生活

was “0used to”是一个时间状语性质的东西，可以省略动词

It was a more difficult life than he was used to, so he had to work hard to support the family.
生活比过去习惯的更艰难了，以致于他不得不努力工作养家
to后省略的是“life”

It was a more difficult life than he was used to, so he had to work hard to support the family.

A. was used to B. used to

choose A

Be used to=get used to＝get accustomed to习惯于
Used to 过去常常，惯常, 惯于 eg.He used to walk to school.

原句的意思是：
现在的生活比过去更艰难，所以他不得不努力工作养家糊口
It was a more difficult life than （the life) he was used to, so he had to work hard to support the family.

the life与前面重复，所以省略掉