I'm new here on the forum and also new to gardening, so please bear with me.
I have owned a Eureka lemon tree since about 7 months. I received it as a gift from my parents and have been using the best of my ability to take care of it.
It actually went pretty well; it kept pushing out new leaves, the leaves looked nice and green and new blossom and buds were growing.
Back in May I went back to the Netherlands (my home country) for about 6 weeks and after I got back I think it was overwatered by the person taking care of it. The leaves were yellow and curled and it looked like it was in bad shape. I purchased a soil moisture meter and didn't water it until the moisture level got at the lower end of the spectrum again. Also since it has been really hot in California the past few weeks I decided to move the tree into the shade after about 6 hours of sun for the day. Since then it started looking better again and I think it's pretty healthy again as far as I can judge.
I left the tree in the pot since I got it, because we are planning on moving to a new house soon and the new house doesn't have a backyard, so we will have to keep it on one of the balconies. It's still in the original pot and I want to allow the tree to have some more space so it can grow bigger, so I want to repot it into a bigger pot.
I already read up on it a little and read that I should get a pot with big holes in the bottom to allow excess water to escape. I also saw those plastic 'things' for the bottom of a pot to protect the roots from overwatering.
My main concern is what soil to use. I read that regular potting soil is a no go and even the special citrus tree soil they sell at the big stores are no good.
I require a sandy soil with a little bit of clay if I understand correctly. Is that right? And where would I be able to buy that? Or should I make my own mixture? And if yes what would I put into this mixture? And do I use compost too? And fertilizer? I have been using the citrus tree fertilizer they sell at Home Depot. Is that the right fertilizer to use or are there better types?
Also what is the ideal pH for the soil for a Eureka tree?
I hope you can give me some advice, because I'd hate to kill this tree when I repot it. I also added some pictures of the tree.