In the UK, we might say 'lounge about'.

"I'm going to loaf all day." This is both good informal English and good formal English. (oxforddictionaries.com includes it as an ordinary word, and doesn't call it "informal" or "North American.") Walt Whitman wrote (using an older spelling), in 1855, I celebrate myself, and sing myself, And what I assume you shall assume, For every atom belonging to me as good belongs to you. I loafe and invite my soul, I lean and loafe at my ease observing a spear of summer grass. Jack London wrote: "No lazy, sun-kissed life was this, with nothing to do but loaf and be bored." John Buchan wrote: "Then I caught sight of a policeman a hundred yards down, and a loafer shuffling past on the other side."

You might use the following synonyms 'to relax', 'to while away', 'to lounge around', 'to doss about/around'.

How about "lounge around"? Someone actually brought up that expression only a few hours ago. It's slightly more pejorative, and often used as a criticism of a person who isn't doing any work. More colloquially, you could say that you're going to "take it easy" or "chill". And more colloquially ( and lazier) still, how about "veg out"?

I can't think of a concise replacement. Anything else has a different meaning.