While I'm nowhere near the need to start toilet training, parents that I know who have gone through this say it’s a pain because you have to fit a toilet seat to your current one when your toddler needs to go.
Trying to make this whole hullabaloo so much easier is the Rymax Family Seat. Designed for toddlers, it combines a standard adult toilet seat with a child-size toilet seat in one.
According to the blurb on the company's website, what this means in practice is that everyone in the family (big or small) can use the toilet without having to worry about fitting certain seats, padded hoops or whatever else you're using.
Coming in either wood or white, the Family Seat costs £30 and is available from bibsandstuff.com an online store for unique and practical baby products.