Angela,
The quality of your work will govern how going vat registered will be perceiveed by your domestic customers.
If you are good then the majority will keep you as good cleaners are hard to find, if you are mediocre, then you will lose a lot to "cash in hand" cleaners.
We went VAT registered a few years ago and I can't remember us losing any customers on the domestic cleaning side.
Put a letter together for all your customers, give them plenty of warning about going VAT registered and explain that you understand the price hike is considerable, but your business is growing, etc, etc.
I think that the VAT threshold should be abolished as it doesn't encourage small businesses to grow and can even knock them backwards, a lot of businesses like yourselves will try and absorb some of the vat costs, therefore losing out on your profit. Don't do this, if you lose customers, you lose customers, you will find new ones, target the commercial market.
Merry Christmas