I'm sure my answer will be different than a lot of the posts, as we seem to approach money differently than most people (even Mustachians), so you'll probably get a lot more than will be relevant to you, but wanted to throw out another viewpoint. :)
We didn't set a budget when working, and we don't have a budget now.
Instead, we spend what we want, and occasionally (months later) look at what we're spending. While working we'd check that number to calculate a time to FIRE (based on a rough guess of how much we
might spend). Now it's to see if our FIRE is sustainable, or if we need to earn more money, or what.
For example, we FIRE'd in June 2015, but (as teachers) received paychecks through August 2015, and then left the states at the end of August 2015.
I didn't look at our spending for nine months, until June 2016. Haven't looked at it since (5 months or so). I'm considering
not even tracking it anymoreIt's just not that interesting, to me, to look at spending or budgets or try to see if the amount we eat out is above or below some arbitrary number we set.
It might be worth trying out, for a bit at least, both before and after FIRE. Spend to a level you're comfortable with.
Maybe not, if you constantly have to reign yourself in currently, every month pushing against your budget and depriving yourself. But if you naturally spend pretty little, are happy with your spending, but want to splurge some... just do it. Track the spending afterwards, so you can look at it, but don't bother trying to hit a budget, or spend except where you want to.
Then check up, see if you're still hitting savings goals (and, after FIRE, see if you're around a 4% WR, or even a bit more, but if your portfolio is trending up).
If you have a naturally frugal mindset/disposition (or one cultivated over years of saving for FIRE), it may work better than you think. It'll reduce your thinking about money, and allow you to have those splurges, without adversely affecting anything.
Like I said, maybe a bit different, but hopefully might give you (or someone else) something to think about. :)