U seem to have diagnosed ur problem and already decided that you need ur teeth to be filled.
So what is the question?
Well, if the cavity is superficial (not involving the nerve, in which case you will not feel pain) then a tooth colored or silver (amalgam) filling will suffice.
In case the decay has reached the root canal (nerve and blood vessel) then complete root canal treatment will be needed.
Next Steps
Consult a good dentist
Health Tips
Delaying the treatment will increase the disease and in turn the trouble and expense. So do not procrastinate!