I think you letting yourself being carried away by your first impression of the language. As you progress you'll realise that Spanish and Italian are more alike than say Italian and French. Italian, Spanish and Portuguese are the most closely related Romance languages (major languages I mean let's not forget Catalan, Rumanian, Occitan and more). Try listening to tizziano ferro, Laura Pausini, Eros Ramazzotti or Mecano, they have many versions of their songs in both Spanish and Italian, listen to them and you'll se how alike they are both in vocabulary and structure. Note: they also have versions of their songs in French....try listening to those too.
I would say that that would be the best choice if you are going to continue studying Romance languages and you are already fluent in Italian. Both languages share very similar structure and grammar but they are different enough that you won't run the risk of mixing them. It would be very unlikely that you fall into a hybrid language, let's say "portuñol" for example. I'm currently taking the Catalan course in duolingo and I do mix Italian with Catalan, even though one would think the mixing would be between Spanish and Catalan . My preference is as follows to tackle the Romance languages offered by duolingo from the easiest to the most tedious : Portuguese, Spanish, Catalan, Italian, Romanian, French. I hope this helps.
Thank you! That was very descriptive, i appreciate the thoughtful answer. I am learning seriously for the first time so it is hard to know what to expect. Honestly im surprised im able to fit new words into my brain and slightly worried of "running out of space". You list Portuguese first, does that mean you find it easiest of the romance languages? That's intriguing.