As others hace commented, tour written english looks pretty good, so don't worry on that front. As a fellow Spaniard (hola!), I used to be in a similar situation. The way I remediated it was by getting to work with international teammates and no Spanish people around, so that you are forces to so no code-switching at all over working hours. Code-switching (changing languagea often) can make full immersion hard to achieve. Some companies in Madrid and Barcelona are fully international, but not many - in my case I found myself in that situation in a research position, but I realize those are exceptional circumstances.