Walikum as salam @MAiken
The Islamic equivalent of bonds are called Sukuks. The one I am aware of is Franklin Global Sukuk Fund. I am myself looking for suggestions on this if any reader is aware of the Sukuk funds in the market?. I have seen this available on Wahed portfolios and simply ethical.
Diversification: Have a look at the IFG Halal Comparison tool but I don’t think that we have shariah-compliant full-blown multi-asset funds/instruments available. Portfolio can be as simple as one global equity and bond (Sukuk) fund or maybe cash ISA at Al Rayan if you want a relatively low-risk instrument. Wahed may be a good place to get a feel of the readymade portfolios if you are interested in the “Do it for me” approach.
Correlation depends on a lot of different factors. You may find this article interesting on the correlation matrix
All the best.