Adding column into MySQL table size 150GB
For 5.6:  pt-online-schema-change is probably your best bet.  It creates a new table with the change, then gradually copies rows over.  Meanwhile, it uses a TRIGGER to keep the new copy updated.

For 8.0:  ADD COLUMN now has ALGORITHM=INSTANT.

Would you like to show us SHOW CREATE TABLE; there may be some improvements that would decrease the problem.