Full disclosure: my mother was a hoarder. I am not but definitely have to be "aware" of stuff to avoid major unwanted clutter (not to mention unwanted spending). The hoarding shows are painful for me to watch but the online board Children of Hoarders helped me a lot.
...it's not like my disposable money is going to change.
- I'm pretty good (not always, but still pretty good) at walking away from temptations, the problem is the longing HURTS and the temptation is hard to resist. I feel like my willpower reserves are not infinite and I just want the wanting to stop.
Sounds like you have already made a lot of progress. Yay!
I agree with the other suggestions to avoid stimuli focused on buying stuff - basically, much of modern media. Luckily there are lots of websites to help reinforce non-buying behavior, I like zenhabits and unclutterer and also postconsumers and earlyretirementextreme.
One habit that might help is to be aware of when you are "longing" and then purposefully interrupt your "longing" interior monologue to remind yourself that you *have* paid down debt and *have* changed your spending habits and *are* preparing for early retirement and actually your life is now better - even use a catch-phrase like "longing passes soon" or "more stuff isn't what I want" or "stuff isn't me" or...whatever captures it for you. Won't stop the longing right away but could help short-circuit it.
...It takes awhile to "reset" the thermostat.
...In fact, I've pretty much had to stop watching HGTV because at one point seeing all the fancy house upgrades actually made me feel sad about my house (which is a very nice house, IMO).
We have a game in our house where we call out each time someone says "need" or "must have" on an HGTV show. Because, you know, humans can't survive without a master bath the size of my living room