get slim
become smaller
get thinner
get slender
become lean

Now, though, the return on the effort of living had become too small.

However, by the end of the 1830s, the chapel had become too small.

It became small enough for him to see completely, then smaller yet.

Already by the mid 19th century, the school had become too small.

By the end of the 1830s, the chapel had become too small.

By the 17th century, this had become too small, and discussions started about building a new one in 1608.

The newer church was built because the old one had become too small.

So too the wise may become great, By becoming small.

The library was useful but within a few decades of use had become too small.

But Lee's voice had become so small and thin, it was lost in the wind.