LA lazy sSunday

Today wasI had a lazy day.

More natural

Here in Zürich it is very cold, I think around -7 degrees, and with those temperatures I don'idn’t want to be outside.

Tense

One of my roommates didmade crêpes for breakfast, and while they were delicious Ithey made me feel guilty ofabout eating all my daily calories before 9 am, so when my friend Ana called , inviting me to go foron a walk, even when I had a lot to study, I had a guiltybecause of this feeling and, I couldn't bring myself to decline the invitation.

We ended up walking for more than 2 hours and it waswe had a nice conversation.

As soon as I returned home, it started to snow again, so I'm glad that I was not outside anymor felt thankful for returning home just in time.

A C1 level description very authentic very native-like; also tenses.

I was not feeling hungry, so I spentended up spending the rest of my afternoon studying and now soon going toI will be makeing dinner soon and prepareing for tomorrow.

Lazy sSunday

Here in Zürich it is very cold, I think around -7 degrees, and with those temperatures I don't want to be outside.

One of my roommates didmade crêpes for breakfast, and while they were delicious I feel guilty ofor eating all my daily calories before 9 am, so when my friend Ana called inviting me to go for a walk, even when I had a lot to study, I had a guilty feeling and couldn't decline the invitation.

We ended up walking for more than 2 hours and it was a nice conversation.

I was not feeling hungry, so I spent the rest of my afternoon studying and now soon going toI will make dinner and prepare for tomorrow.

Here in Zürich it is very cold, I think around -7 degrees, and with thoseat temperatures I don't want to be outside.

or "with that kind of temperature"
But we wouldn't use "temperatures" here because you've only given one temperature

One of my roommates didmade crêpes for breakfast, and while they were delicious I feelt guilty ofor eating all my daily calories before 9 am, so when my friend Ana called inviting me to go for a walk, even whenthough I had a lot to study, I had afelt guilty feeling and couldn't decline the invitation.

We usually use "even when" when describing not one point in time, but a regular occurrence or hypothetical occurrence, for example:
Even when I have a lot to do, I try to answer you phone calls.
Even when it was raining like crazy, my neighbor is out there working on the fence.

I wore all the warm clothes I could think of, and went out.

I would use a comma because "of and" sounds awkward to read in succession without a pause.
Also, I would probably write "I wore all the warm clothes I could find", but, that's slightly different from what you said.

We ended up walking more than 2 hours, and it was a nice conversation.

The clauses are separate so I think a comma is pretty natural between them.

I was not feeling hungry, so I spent the rest of my afternoon studying and now soon am going to make dinner and prepare for tomorrow.