Having been involved with the postal system for more than 30 years and now providing mail forwarding services for boaters I fully sympathise with your situation
If you go back to the Post Office where you had Poste Restante, can you not talk through with the owner of the shop to the effect that if you can receive your post there, you will be reguarly coming into the store to buy things
You will have the issue that government (driving licence) and banks will not normally accept a Poste Restante so you will need a street address for your mail - will friends hold your mail and you collect at sometime? If you have friends locally, you will be able to set up a Royal Mail PO Box by using their address (expensive and going up again in price) - you need a street address to set up a PO Box
Royal Mail Delivery Offices do not accept mail for collection without having an associated street address in the delivery area
You should be able to reduce your mail volume by moving most items on-line. If you use a mail forwarder, you will find that some of them do not charge a monthly fee asking you pay by item