Asking for puppy + life advice

Hi, i don't want to beat around the bush here, but i guess i am in the puppy blues.
I have a 10 week old puppy – bearded collie x miniature poodle mix. Me and my partner have wanted a pet for a while, and when we met this puppy we thought we just had to add him to our lives, it felt right.
We've had him for over a week now, and although I understand i am in early days, and puppy blues is a real thing, i cannot get over the idea that i may have made a mistake in life.
I am in my late 20s, decent job, living in the city in a rented flat/apartment. I work remotely; my job is extremely important to me, and i put my all in each day.
The hard part i am dealing with at the moment is I went from doing nothing – working all day, small walk outside, get food, back home for a movie and chill – sleep really well each day – to going up and down 4 flights of stairs to the garden and back to my flat multiple times a day: 7am – 8.30am – 10am – 13:00 – 15/16:00 – 19:00 – ~23:00. Thankfully the puppy sleeps/is quiet for the entire night.

4 flights of stairs does take a mental toll on me, it's a big mental blocker, there are other things that take a strain like him crying each time he's in his crate during the day, but I know those issues will fizzle out with time and repetition of practices.
I looked online for my city (in the uk) and i can barely find any properties to rent that allow pets and have a garden. I feel locked down completely! I feel like my choices are stairs each day for years or having a serious talk if this is the life i want to live. This is clearly a big lifestyle change for me, and it could be worse (he could wake in the night), but i just can't get the idea that i cannot not go out the flat, cannot go to an office without worrying or paying money for a sitter, cannot go out for dinner, cannot go do anything random anymore.

Does anyone have any advice on what kind of routines that i could use in the future to help me? Anyone live in a city without a garden/poor accessibility to a garden?
I'd like to know when he is older, will it be easier? Will the dog be able to be calm in the flat for majority of the day, and go on 2-3 walks per day as a routine?