I have a FSA 52/36 on front and ultegra on back. Any thoughts?
Are you sure about those chainring sizes? The 36 inner ring would seem to indicate a compact crank with 110 BCD. But compact usually have a 50 big ring instead of a 52.
For us to give you a good recommendation it would also help to know the size of the cassette, smallest and largest cassette cogs.
Usually the most cost effective way to lower gearing for a special event is to change the cassette and rear derailleur to mountain gearing. If you have a 10-speed cassette you will be limited on mountain bike cassette options, Shimano does not make 10-speed mountain bike cassettes but there are some available.
If your inner chainring is indeed a 36 you could change it to a 34 but you would then need a 50 or 48 big ring.
Going to a triple would require replacing the crankset, bottom bracket, both derailleurs, possibly new shifters (depending on what you now have) and probably a new chain.