I feel guilty for not providing a perfect life for my cat

I love my cat, (2 years old) but I work during the day and I havea normal student flat (30 m sq). She's really energetic so I'm worried she is bored out of her mind or lonely. When I go away, which is often, I drop her at friends so she's taken care of and she gets a change of scenery. She seems to be fine with it, she's very social and she loves exploring new places. I live in the busy city centre so I can't let her go out... There are tons of cars and strays that fight. I have put up "cat shelves" on the walls to provide some stimulation and more space for her to roam around plus she has some toys that she can play with when I'm not there but I hate that she gets bored. I definitely want to get a bigger place at some point and get another cat to keep her company but it won't be possible for some years.