Yeah, I'm not a finance wizard, such as yourself. I always envisioned sort of a three bucket approach. Bucket 1 would be three years worth of cash/fixed income, like CD ladders or whatever makes sense at any time. Bucket 2 would be 5 years worth of...something...like bonds I guess. Then bucket 3 is equities. Rebalance the buckets based on market conditions. Bucket 2 is what I've struggled with knowing how to handle. I've never really known how to properly invest in bonds, and obviously I need to figure that out.
You basically have two options, buying individual bonds or use bond funds.
There are advantages/disadvantages to each. If you are someone who likes to dig in, and wants to build the most efficient possible setup....then learning about individual bonds may be worthwhile. You could build a bond ladder just like your CD ladder, save on fund expense costs, more closely match timing that you would need the funds etc.....
But buying a bond index fund (or funds) is definitely "good enough".
Two risks in bonds....credit risk and term (duration) risk.
You can eliminate credit risk by buying Treasury bonds/Treasury bond funds. If you want more risk in the portfolio, just buy more equites. Don't need to take credit risk on your fixed income side.
You can't eliminate term risk, other than buying shorter term bonds/funds...but typically that means lower return. Standard portfolio management is to match the term/duration of your bond investments to your investment horizon. That was what I was referring to as liability matching. So maybe have some 3-5 year bonds, and maybe some 10 year.
The only "problem" with bond funds (mutual funds/ETFs)...is they are going they are going to continue to roll maturing bonds back into new bonds. So your duration never really changes, when maybe you want it to be getting shorter. Just a lot of moving targets and ideal setup is going to vary a lot based upon the individual circumstance, tax bracket, etc..
TL/DR/DGAFF....just buy an intermediate term Treasury bond fund with low expense ratio.