The Triban 3 has mudguard eyelets so it would be best to fit some traditional guards in 35mm width such as SKS Chromoplastics, SKS Bluemels, SKS Commuters or Tortec Reflectors. It will take a while to fit them so give yourself plenty of time. Black or silver would suit your bike well.
You'll need to cut the stays with a hacksaw or bolt croppers. It's best to fit them on to the bike then mark the stays with a marker pen where you want to cut them. My top tip for rattle free guards is to mark the position where the rear bridge will sit on the guard and then apply some "No more nails on a roll" tape under the bridge and under the guard where the bridge clasps the guard. You should also fit them in such a way that there very little tension on the stays: this helps to prevent them cracking going over bumps and stuff. A little Locktite on the screw that attaches the rear guard to the chain stay bridge will also help keep them securely fixed.
You could also go for something like Crud Roadracers, but these are a little flimsy and more likely to go out adjustment and rub. Seems daft to fit this type of guard to a bike with eyelets, but these are decent enough guards and have great coverage. Make sure you apply plenty of insulating tape where you attach the cruds to the bike stays and forks otherwise they will mark the paintwork over time.