I have some rooms in my house w/ solid 3/4 " strip (2.5") installed directly over 19/32 OSB. I would like to do an adjoining room with 3/4" solid 4" plank flooring stapled down. Would this leave me too subject to gaps between the wood?

Is it worth the additional trouble and expense to lay 1/4" luan with a 1/2" engineered product instead? Or should I just stick with teh 2 1/2" strip hoping this would hide more errors?

This would be my first DIY attempt. The subfloor incidentally has some high spots at seams I would need to sand.

Thank you.

luan never lays flat unless glued down...and even then it's questionable. and, if it ever gets wet...kiss it good bye.

my humble opinion only

Since you already have a 3/4" solid nailed down over 5/8 OSB without any problems I think you would be Ok with the 4" plank. This has more to do with the inside environment and humidity levels than it does with whats underneath.