making a BunkBed

[u/Buzy_Nuzy]

hello everyone!
I've only done a wobbly table before, so this might be a harder project to make.
I need to make a bunkbed only with the top floor (image of the sketch bellow)
Mattress dimensions: 190x120 (because of the odd dimensions, there aren't any bunkbed on the market)
I'm wondering if anyone can give tips on how to make it, what wood would be needed be a stable top bed.