Hi and welcome to Beoworld.
First of all, replacing the woofer surrounds on the CX100 is not that difficult if you’re a little bit handy or careful. If you’re good with you’re current setup, that would be the better option. The process is very well documented all around the internet, cheap, and kits come ith all you need to do it right.
If you don’t want to do this I’d look at the second hand market for old or less older Beovox: CX range (but be sure to check the surrounds and listen to the speakers) or depending on your tastes, RL, Pentas… On some models same checks apply than for the CX.
Unless you like the look of them, I don’t find BL18 (that I love) will look nice next to a BC8000, less than 8000 if you really want columns. Using standalone systems like levels, Balance or similar is to me, a waste and as you said, not a really convenient solution unless you reaaly want to use the wireless connection as main source.