any proper pond switcher with CE markings will be fine, seems more you spend the better you get in terms of quality. I have a something or other powersafe three way - green, bought from ebay for about £30.
you can wire it in yourself, assuming the suitably sized cable is on a 13amp domestic plug, plugged into a circuit on a breaker within the house/shed/wherever the nearest power is. This is a gap in the law as it is classed as 'tempory', like wiring a plug yourself on any domestic appliance and is technically protected by the houses consumer unit.
ideally and best, would be having it hardwired to an RCBO/MCB on a consumer unit (box with all the houses breakers in), with a proper armoured cable to the switcher. This must be fixed every 40cm to a perminent object (such as a fence or wall) or buried 1ft to conform to British Standard regulations. This is a perminent outdoor installation - must be done by a professional. It means however, that the cable is pretty mighty so your spouse when out digging in petunias will be unlikely to pierce it and shock themselves, and that it is on its own breaker which will trip if anything especically on that feed goes mad.
We had a garage to office conversion done in the summer with our building works (when we had a digger for the pond too), so when i installed a supply to the office, i ran a 1.5mm armoured cable from a 10amp RCBO straight out the wall and under the lawn to the pond. All nice and safe and should easily outlast the ponds lifespan.
I also, being a lighting technician in the live sector, sent three more armoured runs out to other parts of the garden, two for garden LED lighting - one on a wooden doorframe style grid thing along a path and one to the location a summer house will be constructed in the summer, and the third going to a 32amp ceeform outlet for any time i may decide to do some welding, or light up the entire gardens features for a garden party type event - 7600watts of it!
If doing the proper option, id look into what else you would like powered while the sparkies there and get it done in one lump. Its hardly any extra work and wouldnt cost much more, and would give options to upgrade in the future.
hope this helps, pat