"Ones" as a Pronoun

I'm trying to explain to some EFL students how to use "ones" as a pronoun. This is what I came up with:

When "ones" is used as a pronoun, it usually refers to things of a particular type within a group.

A) Do you like doughnuts?
B) Yes. I like the ones with jam in them.

Group: doughnuts
Type: doughnuts that have jam in them

A) Do you like movies?
B) Yes. I like ones with happy endings.

Group: movies
Type: movies that have happy endings

A) How many cars do you own?
B) Three - a blue one and two red ones.

Group: cars
Type: red cars.

A) I can only afford two CDs.
B) Which ones will you buy?

Group: CDs
Type: CDs that 'B' will buy.

Do not use "ones" in place of "more than one."

A) Do you own a pet?
B) Yes. I own ones. (INCORRECT)
B) Yes. I own more than one. (CORRECT)

If 'B' were to answer, "Yes. I own ones," 'A' would think, "Ones what? Ones with fur? Ones with feathers? I know that the group is "pets", but what is the type?"

END

Is there anything drastically wrong with this explanation? This is the best way I could think of to explain how to use "ones" as a pronoun. The important thing is that they understand why "Yes. I own ones," is incorrect. Any help would be greatly appreciated.