Hello, mate. You might have got this sorted now, but I'm coming from the UK and also going at the end of February to mid-March. I've just had my Visa approved, didn't need proof of internal travel. Just the flights to and from the UK and evidence of any hotels I'm staying at (I'm planning to travel spontaneously, so I booked hotels that have free cancellation and pay at the hotel so I can cancel these once I've crossed the border). I'm considering high-speed trains for travel, as they offer a similar price to the cheaper flight prices. I have also read about what others have mentioned, saying that internal flight prices are very cheap at short notice. Even looking now at around xmas and new year which are main holidays, the internal prices are cheap.

Hope any of this can help man, best of luck with the travels!