Hi there. I could do this for you with pleasure. My name is Rob Jones. I'm a musician and producer based in the UK. I run a small but well equipped studio here where I work as a freelance composer, producer and session musician (guitar/vocal), and I also work with local musicians on a variety of projects.
I can create any additional instrument you require, whether drums, bass, guitar, keyboard. I have a MASSIVE library of high end virtual instruments which contains an almost unlimited sound library.
There are many ways to approach this project depending on what you want as the final product. I can take what you have and add to it as the easiest approach. But ideally we would re-record it all separately and to a click track. I noticed the timing adjusted throughout a little bit - it always does in a live performance! So this is why I would re-record. It certainly requires bass and drums, but I would also suggest some keys, maybe a nice pad sound in the background which swells in the more powerful parts.
But I would work WITH you. I would involve you at every stage. A lot of folks here will take the song, work on it and deliver it with little contact with the client. I'm happy to do that if the client requires, but mostly I find projects develop better with full communication throughout.
As a musician myself, I come at this with an understanding as well.
Feel free to ask any questions.