As I said plumbing is not my thing, my knowledge lies elsewhere in the industry. My understanding is you would use either an accumulator or a breaker tank, pump set and accumulator. The break tank is usually installed on the inlet to the property, away from areas of quiet interest due to pump noise and pumped thereafter to the dwelling outlets. You are sizing for both hot and cold pipework distribution, so the breaker tank will need to be sized correctly. This also provides a short fall should your incoming mains be subject to problems ie, work being done in the street. If pressure is ok (in your case borderline) then you could get away with just a suitably sized accumulator. With the pump set you are solely relying on it to provide the pressure and flow to the property, with the accumulator making use of the energy provided.
As I and others have said above, your incoming supply should have been the first thing to check when considering this type of system, quite often and what seems to be your case is the incoming mains to house will not be sufficient and upgrading is necessary, the bigger the supply line the better, pressure will be whatever it is by the provider but your flow rates will be much greater .