External Door Frame sizing and advice please.

[rgregson1919]

Hello all
I volunteered to change my partners external front door and frame. The cill is completely rotten and the bottom of both jambs too.
I am thinking it’s easier to change the whole frame and the door too as she wants a new one. The current door is standard 2032mm x 813mm.
Regarding frame sizing, I am not sure what is best. The brick opening is 935 x 2160.
I found a frame here which is 901W x 2117H. That would leave 43mm to fill height wise and 35mm width wise.
Is this acceptable?
I am trying to get it to match the neighbours as it is immediately adjacent and am a bit concerned about the 'look'.
Would I build up with mortar on top of the cement plinth? If so, what mix?
From the picture, I see about 20mm of fill on the original frame.
Thank you in advance for any advice
Door frame here:
https://www.expressdoorsdirect.co.uk/door-frames/external-door-frames/external-hardwood-door-frames

 

[^woody^]

838mm is a standard door which uses a 920mm frame which will allow you 7mm each side for packing

 

[rgregson1919]

838mm is a standard door which uses a 920mm frame which will allow you 7mm each side for packing

Yes, that would be ideal but I am having trouble finding a frame to match the vertical height. The closest, I could find was the one I mentioned.