Depends on what you are after. Do you want to pick out your own stuff or do you want a tailor made furniture pack?
If you are after a pack, Arca in Torrevieja are excellent and will come and fit it all for you in a day including putting units on walls etc.
One of the best (and reasonable) places for picking out your own things are Hnos Garcia, also in Torrevieja. They have a website (with prices) so click the word here .
There is also a very good shop (but a bit more expensive) on the left of the roundabout as you enter Los Montesinos.
Arca and Garcia will deliver in a day or two (maximum we have waited when it is not in stock is 4 days, everything else that day or the next). Not sure of the one in Montesinos.
Also, if you head on the AP7 towards Alicante, there is a discount furniture shop on your left about 5 or 6 miles along.