Hobbes wrote: Just enough to smooth out the electrics and give me enough time to save my work and shut down in case of a power cut.
So your current UPS is an always on-line pure sine wave output one? Because most small UPS systems aren't and the battery (and associated voltage regulation etc.) only kicks in on power failure. These typically start around the £1000 point in the UK.
Tell us the model you have, then it's easier for others to suggest something (not that I 'm current with UPS offerings).