Unless you overwrite/change the default bas redirection settings, you will have more bas from two BL9 than you can ever get with the BL19.
In some cases you might achieve a better/more uniform bas reproduction in the room by keeping the 19 (e.g. in the back of the room) and by tweaking the redirection settings (have a look at the Technical Sound Guide if you want to dive into this).
However this is not for ‘beginners’ and probably won’t be needed in your rather small room.
Tip!
Be sure to make different Speaker Groups for video and for audio listening (for this also see the Technical Sound Guide).
P.S.
If you don’t need surround and rear speakers in the new room, you could use one set 18’s and the 19 in another with a BS Core or alike.
MM