Personally, since I don't have that much to save in bonds, I have been buying a lot of I-bonds
There are several nice discussions of the max downside of bonds on the Bogleheads forum. After reading, it is not a scary as I once thought. Personally, if I had a lot of money in longer term bonds, I would capture the gains now and move to shorter term bonds of some sort. Of course I did this last year with about $10,000 and I missed out on quite a bit of upside. But, I don't regret it. To me, bonds are for safety and I take my risk on the equity side.