Originally Posted by mstateglfr

10 speed tiagra 4700 wont work as it has a different pull than previous tiagra STIs. Same with the new sora r3000.

With that said, if you get STI shifters where the cables exit the side of the shifter in the middle of the bike(vs hidden under tape), you should be good.
This means older ultegra or 105 will work too. Keep it to 9 speed and there will not be a problem at all.

You will of course need a new cassette to match the # if cogs to the shifter speed.

Also- if you want to consider Microshift brand shifters, they make excellent 9sp shifters for the money. I have some 7sp shifters made by them and the 9sp is the same quality and functionality- really solid and good price.