Hi sooby, thanks for the warm welcome :)
> Did you just move it up into a bigger pot or did you remove the original potting mix from the rootball?
We moved it to a bigger pot together with the old soil. Filled the remaining space with 50% heavy garden soil and 50% general compost with peat. After a few weeks the tree "sank" into the soil a bit (maybe we didn't press it well when potting?) so I removed some soil from the top.
> When you set it outdoors in the sun after it had been living indoors, did you introduce it gradually to the different environment?
Took it out right away. Its new location was just outside the patio doors (it was behind the doors before) in a corner where there wasn't much wind.
> A pot should have drainage holes
I hang my head in shame and admit right off that I started with zero experience. The pot doesn't have holes. We have a few other pots like this one which we have now drilled. We haven't drilled this one yet out of fear of upsetting the tree further while taking it out. The soil is only slightly moist now.
> can I ask why you are keeping it indoors, which is not ideal for it?
Just ignorance. If it survives through this it will sit outside permanently