We also live in a 3 storey house.
We use the Tomy Walkabout Premier, which has been excellent.
It has a 250m range. It can be bought from B2B or Mothercare.
Neha
I suggest that you buy the Tomy monitor from B2B with a view to trying it out first and exchanging it if you don't like it. Please see my comments on a different Tomy model in this thread: http://www.geobaby.com/forum/thread122776.html
Hi Neha, I just bought the Tomy Walkabout from Bumps2Babes -its got a 300 metre range and its working well so far. It came to about $460 with the members discount card and they did say I could bring it back within 14 days with original packaging and exchange if it didn't work.