Wholegrain flour doesn't produce as much gluten as bread flour, so it won't trap air as well (resulting in it being flatter). I doubt it was because you didn't have enough water -- in fact if you added water until it was sticky you probably added more water than you did for white flour (wholemeal absorbs much more water).
As an aside, for anyone confused why recipes online can have 70% hydration (when 50% hydration for your dough makes it much sticker than reasonable), it's because they mix wholemeal flour with bread flour and don't mention it in the recipe. I'd suggest adding wholemeal flour (but not much more than 30% of the total flour because too much reduces the amount of gluten you get and thus the structure is noticeably more cakey) because it really improves flavour.
I make bread with 80% hydration: 500 g plain flour (11% protein) definitely no wholemeal, 400 g water, 8 g salt, 1 g dried yeast. Mix roughly leave covered for 12 hours at room temperature (that's between 15 C and 20 C at the moment), cook in a preheated pot with a lid for 30 minutes at 230 C, take off lid, cook for 15 minutes more.
well the first bread was probably ⅔ wholemeal (500g) and ⅓ white (estimated) and 350ml water. i started with wholemeal only and the result was still very sticky. but maybe i just didn't knead it long enough for the flour to absorb the water.
the second was surely less water although i didn't measure.
> but maybe i just didn't knead it long enough for the flour to absorb the water
If you let the dough mix sit for a 10 minutes or so before you start kneading, it allows the flour to hydrate and thus it'll get less sticky. This is one of the arguments for "no-knead" bread recipes.
But when kneading bread you should always knead it until you can take a piece of dough and stretch it thin enough to see light through it (this is called "the window-pane effect"). This indicates that the gluten in the dough is strong enough for a good rise and crust. Once you knead it to that point it's almost always no longer really sticky.
That's okay, you can mix it by hand and it will work without issue (it's what our ancestors did for thousands of years). But if you don't want to knead for 10-15 minutes, if you roughly mix the water and flour then wait 10 minutes and then start kneading you'll find it takes much less time and effort to get the same result.
As an aside, for anyone confused why recipes online can have 70% hydration (when 50% hydration for your dough makes it much sticker than reasonable), it's because they mix wholemeal flour with bread flour and don't mention it in the recipe. I'd suggest adding wholemeal flour (but not much more than 30% of the total flour because too much reduces the amount of gluten you get and thus the structure is noticeably more cakey) because it really improves flavour.