My lo was exactly the same when I changed to mixed feeding!
i tried to do at least 3 hours inbetween but gave in of nothing else worked including boiled water! If they are hungry then they are hungry! This went on for about 5 weeks and now suddenly she is happy to go 3-4 hours in between mostly, even if she is awake! I also have found the dummy helps to comfort her as sometimes she wants to suck for comfort not food! She was also doing the silly feeds, and my opinion was to judge what she took over 24 hours in total rather than one feed! She wasn't taking anymore than recommended!
The last week she has also now started taking 5-6oz each time which is great! She is 9 weeks old.
Your lo will probably grow out of it and gradually go longer, but it may take a few weeks. Just keep going with what he wants, and so long as he is content and putting on weight and having wet nappies it will be fine! It is definitely worth trying the boiled water first before food - but definitely give in if you need to!
Re making up the bottles, you can make all the water up in advance and leave it at room temperature and then just add the powder when needed! That is what I did as her feeding was so erratic! It saves so much stress and screaming

Good luck