Just get a big tub of Zinc & castor oil creme from the baby section of Boots for a couple of quid. No need to mess with making anything. I haven’t used anything else for years.
I had a big tub of E45 and last year used it as chamois cream when I did all the turbo riding in the garage. I could barely tell any difference in the that and the regular stuff.
It doesn’t smell lovely like the Rapha stuff but at least you can get the last bit of E45 out of the jar.
Bag balm’s great stuff, for sores, but it doesn’t really have a good consistency as an actual chamois cream. I think chamois cream needs are different enough that you just try them, exactly how slippery you want will likely depend on your arse, your shorts, your saddle, how much you sweat etc.