According to my incredibly useful new “Knitspeak” book, Super Bulky is anything that knits on 8mm or larger needles and the best way to substitute a yarn is to choose one with the same ‘gauge’ (i.e. tension square) on the label. Something that’s about 8 stitches to 10cm is what you want - Rowan Big Wool is about that but not exactly what you want for a baby item. Sirdar Wow also looks like it’s the same gauge but states smaller needles… hmmm…
Other suggestions:
Stylecraft Alpine Super Chunky
Sirdar Denim Ultra
Twilleys Freedom (more stitches to the 10cm but on 10mm needles)
If you have a LYS, go in there and tell them you’re after a similar weight wool and hopefully they can steer you in the right direction!
BTW, I don’t profess to know much about this - just been doing a comparison on the interweb! lol