I went through your bits, but worried that it would be too top heavy even before an unruly toddler clambers up, then found the spare 20x30mm. Plus it should look more in proportion, whereas some of the Ikea hacks I've seen look a bit chunky up top.
Although it's rough as fuck I sanded a section of one of the better bits down and it came up OK.
Cheers
It's actually this stuff: https://www.wickes.co.uk/Wickes-Treated-Sawn-Timber---19mm-x-32mm-x-3m/p/9000036476
I went through your bits, but worried that it would be too top heavy even before an unruly toddler clambers up, then found the spare 20x30mm. Plus it should look more in proportion, whereas some of the Ikea hacks I've seen look a bit chunky up top.
Although it's rough as fuck I sanded a section of one of the better bits down and it came up OK.