What would be the best replacement shocks and springs for my Lexus LX470?

What is your question?

I have a 1999 Lexus LX470 that I need to replace the suspension on because the current air suspension is shot. I am wondering how I should go about taking the shocks off if I need new springs (there are only springs in the back), and what new shocks/springs would be the best for a budget of about $600? Right now, when I drive over bumps the suspension feels really loose which I have been told is a sign of worn-out suspension. The car has about 110000 miles on it if that is important. Let me know your opinion! Thanks!

What makes this problem better or worse?

I haven't really driven it enough to know if there is any effect at all in different conditions

How long has your 1999 Lexus LX470 had this problem?

They have been shot for almost 3 years but not driven during 2.5 of those 3 years.