The big plant is 5cm thick now, I've been trying to thicken it for a long time and had some success. So I will probably leave it. I just like to know my options.

Some plants will 'thicken' their trunks easier than others. 'Bonsai' style would be thick and tapering. It needs patience and careful pruning...In my limited experience, finger jade wll taper better than 'regular' green-leaved jade; both will thicken eventually.

May I ask what do you do to thicken the trunk?

I have jades with trunks over 10 cm circumference - but that is at the soil line and do not need ro be pruned there. This one is approx. 22cm at the base; it has few low branches that I should prune off. Thickest branch (on left) is approx. 8.8cm circumference where attached:

I will (one day!) prune all 3 off and re-root them. I think thickest branch I pruned off and re-rooted so far was approx. 7-7.5cm circumference

I have done a little pruning on mine to keep it short and it's around 6-7cm at the base. Much smaller pot though.

Keeping the lower branches I think really helps.

Nice to see you Kevin...

That is nice, compact plant. Looks like Finger jade - is it?

Well, I changed my mind about shortening it for now when the center showed new growth, this should fill out the middle nicely I think.

While it should help thicken the lower area too without letting it get any bigger.

I believe that if you want to keep it short and full, it should be pruned. This is good time to prune, new growth will appear almost instantly. And it will be much fuller all over. I would prune it something like this to keep it short:

It really depends on what you want to plant look like eventually. BUT this is JMO, I am just reacting to what I can see in photo you posted (full plant would be better), and what you said, and could be wrong.