Tripp Trapp - what bits do I need?

[LittleLadysMama]

I have 3 second hand tripp trapp chairs in my hallway - it was a buy them all only option and the price was too good to refuse. I'm planning to strip and spray them (if I ever find the time) but they didn't come with a full set of accessories.
I'm wondering what I need and the more I Google, the more confused I'm getting!
My little one is 18 months.
I've looked at the harness online but not sure if that should only be used with the baby set? I'm thinking my LO is probably too big now for the babyset but wouldn't be happy to let her sit in it freely quite yet 😳
I know there are different models throughout the years of the chairs and I'm just at a bit of a loss as to what I need at this stage for my girl.
Any advice or images to guide me would be much appreciated! Thanks

I had one from 6 months. I used the baby set until about 2, I used the harness with the baby set once she started to climb and then for a while on it's own with no baby set, probably until about 2.5 but I'd use it on and off, it was a good way to transition to sitting on her own.

Thanks @SandAndFog thats good to know.
Someone locally is selling the cushions, harness and front big of the baby set - not sure why the back isn't included and I'm assuming you need that?
Also worried incase the chair i have has older attachments so won't be compatible with the harness etc. Might see what I can find re models on the stokke site

The original version did not have a high back. Just a front bar and cushion