As with all things the novice is always wary of not doing the correct thing, quite rightly so, and wiring problem posts appear on the forum regularly regarding wire sizing.
The definitive way to calculate the size/ current capacity is to measure an individual strand diameter and count how many individul strands make up the cable, hence the cable you are looking at is designated as 28/0.03 and this is a cable made up of 28 individual strands of wire each being 0.03mm in diameter. Most retailers indicate a wire size by the number of strands/ thier diameter ( 28/0.03) and the mm2 size (2.0mm2) in this example, this sizing method is quite universal.
So in your case cut open the wire you want to replace and count/measure as above to get the wire capacity, then look at the retailers information to match your cable size. If a direct option is not available go to the nearest size UP never down.
When splicing cable a good mechanical and electrical joint is important, whether it is an crimp type, wrapped or soldered, and if replacing several cables in a loom stagger these joints as it makes for a neater job when the loom is retaped.
Confidence will come with experience and every day is a school day for all of us.