I would recommend an un-vented cylinder and tank possibly pumps. The serviceing / maintance costs are less then a combi. The biggest combi I would recommend is an Atag 51c which delivers 23 liters per minute but would cost you around £5000 installed and an un-vented system would be about £4000, also with a system in the future at some point the boiler will break down if you have a system at least you have an immersion heater.
Heating and hot water are not important until they don’t work, that is the time when people realize how important they are. I understand that people are on a limited budget but to go the cheap way is... (How can I put it politely) not very intelligent. You would not by a car because it’s cheap (but maybe you do). The intelligent was it to look at the running costs and reliability. The general consensus is that Mercedes cars are very expensive but if you were to buy a 3 year old lower range model and you calculate the costs over a 5 year period they are actually one of the cheapest to own, also when you get in it you know it will start, its more comfortable and had better prestige than a cheep car.
Find a recommended installer and the best boiler.
Spend less money now and you will certainly pay for it in the future.