Converting to a triple is usually feasible but there can be pitfalls. If you're not experienced with bikes and machines in general, it might help to find someone locally who is, to help (i.e. a friend or bike co-op; you don't want to pay a LBS to engineer a triple conversion for you). Or if you're willing to roll your sleeves up and learn from experience, you can dive in and see what happens. We'll be here to help.
Things to consider in a triple conversion:
Front derailleur range - can the existing FD acommodate the tooth difference, and the lateral movement required?
Rear derailleur chain wrapping ability - can the existing RD wrap the additional tooth difference resulting from the new small chainring?
chainstay clearance - does the frame, existing bottom bracket, and chosen triple crankset, in combination, allow clearance between the small chainring and the chainstay?
If the answer to any of these is no, additional replacement components that alleviate the respective fitment issues will need to be identified and purchased.
there is a secondary issue, chain length; it may be necessary to modify (most likely shorten) the chain, in order to optimize length for the new drivetrain. That is not a big deal, just requires an inexpensive chain tool and moderate skill to use it.
That said, I have done 3 triple conversions, and the only component I've had to upgrade other than the crankset, in one instance, was an FD, which did not have enough lateral range for the triple crankset.