We have a 900x900 shower and it's plenty big enough. Neither of your proposed layouts looks that great, to be perfectly honest, sorry! In the first layout, you could improve it quite a lot by swapping the toilet and vanity (centre the toilet under the window on the bottom right of the picture if possible), and having the shower door on the other wall (beside the door). Then, you could have a towel rail on the wall beside the door (i.e. behind the door when it's open), which would be accessible from the shower but hidden when the door was open. An 800x1200 shower might be a good size for your space. You'd have to choose a toilet that doesn't protrude too far, plus a narrow vanity. With that layout, you could have a long but narrow wall-hung vanity, with a big mirror covering the wall between the windows, which would make the room feel bigger and would give a good amount of storage. Also, you may find this helpful: http://www.houseplanshelper.com/small-bathroom-floor-plans.html?utm_content=buffer4aa20&utm_medium=social&utm_source=facebook.com&utm_campaign=buffer

always prefer separate toilet with handbasin, the bathroom has plenty of space for generous fixtures up to the sizes shown but the bathroom should be planned to suit potential users and relative to the whole plan (where are the windows?) next door rooms, orientation, outlook etc...this is one suggestion that has the best view on entering the room with the shower (tallest) at the side, bath with potential view, vanity with option for two basins and matching mirror doored wall cabinet and the toilet handbasin next to the shower keeps the plumbing sounds away from adjoining rooms more details may inspire other suggestions

I didn't like any of the stock standard vanities I saw being sold. By chance I happened to see a second hand vanity being sold on FB so I brought it ( see photo). I liked its shape and solid profile but didn't like its colour. I took it to a auto car spray painter and had them spray paint it in Benjamin Moore Kendall Charcoal (a greige grey). They did an awesome paint job with a mirror like finish. I brought a piece of primestone (marble look) for the top, two small towel rails to be fixed in the underside of the vanity that is sticking out so I can hang hand towels on either side. I brought a new tap for it (but kept the vessel basin). I ordered in some new legs for it online because I didn't like the legs on it (see below). Its currently at a joiners getting put together. I've actually enjoyed the process of pulling it all together. Sure by the time it has been put together I probably would have spent the same amount that it would have cost me to do a custom vanity however I think there is something to be said for re-using something a second time round rather than buying into consumerism that abounds us. All up I've spent $1,074 NZD for the vanity, the spray paint job, new legs from www.prettypegs.com, the new towel rails from Reece Plumbing & buying a new Elementi tap. That doesn't include the joiners costs - yet. I needed storage in my vanity. This one fit the bill for me. Good luck with what you choose to do! I am doing a bathroom remodel as well and enjoying it.

Depending on latches and fixing area, etc - you could get a good glazier with a bit of finesse to custom make a mirror to fit into the window area, and then just centre the vanity below the window. Provided the window glass is obscure, it will still look like a window from the outside, but you'll have an interesting recessed mirror in your bathroom! (hope that makes sense) But, If you want a seperate shower then it looks like you'll have to alter a lot of plumbing anyway, so you might as well move the vanity while you're at it.