Easiest I could think of was the Besser Block approach. I'd never tried it but though it would be the strongest for a somewhat narrow bench.
Went down the local paver store today and grabbed a few blocks. My god were they heavier than I expected. I drove home with my car's exhaust nearly scraping along the road.
Grabbed a old plank of wood I had at home that was around 250-300mm wide. 15 minutes later and presto! Simplest bench you'll ever make and very sturdy too.

PS. The new trees are the ROR trident and the callistemon subulatus (the possums love me for bringing this home, will hopefully be less appetizing on the new bench

Cheers,
Pearcy.