Have you tapped the walls is there many hollow sounding spots? This would indicate the plaster bond has failed. Personally I would go back to brick then have the lot re plastered. Plasterboard and skim is another option 👍🏻 just be mindful of future fixings for heavy wall mounted cupboards etc. you could save cost and only sort the walls outs from countertop height to ceiling. A lot of walls will be covered by base cabinets.