Someone on 65K with student loans and a pension is taking home closer to £3200 than £4000. I take home £3200ish.
Mortgage = £1100
Service charge = £180
Bills inc food = £600ish (I have a health condition and need to eat well)
Travel to work = £200ish
Average monthly prescription cost = £20ish
Phone = £10 (bought cheap handset outright)
That's already £2110 just for pretty much bare minimum monthly essentials to survive.
Netflix, Amazon Prime and Spotify (basically my entertainment because I rarely go out) = £30ish
Gym membership = £50ish
Toiletries/skincare (inc toothpaste, mouthwash, lip balm, hand cream, shower gel, tretinoin, moisturiser, sunscreen) = £30ish
My non-essential recurring costs total about £110, which I don't think anyone could argue isn't ridiculously low.
That's a total of £2220ish, leaving me with £980ish a month. That goes into:
Emergency fund savings = £500
Holiday savings = £300
Misc expenses (going out, very occasional drinks with colleagues, unexpected costs, gifts, haircuts, dental work, travel to see family etc.) = £180ish, so just under £50ish a week. One single train ticket to see family can be £100 return. I just spent £250, so well over my monthly budget, on a nightguard for grinding from the dentist.
Is any of this decadent to you? Because it certainly isn't to me. I have to think about money constantly. The idea that I could afford a drug habit on this salary is hysterical. The only remotely decadent thing I do is go on holiday, and considering I don't have kids, I don't think I spend that much on it.