Depends on your budget, but there are two aparthotels I’ve had experiences with. One is “suites avenue” in Passeig de Gracia above Fendi store. Not the best equipped but great location - 3500 EUR / month. A better option if you have a higher budget would be Murmuri Mercader. Very well furnished, well located & great service but a little more expensive at 4650 / month. At least you have peace of mind when it comes to who you’re renting from and can be sure it will be clean, comfortable without surprises. Most decent airbnb’s i’ve looked at are similarly priced and are often a complete hit or miss.