A 45-year-old man presents with polyuria, polydipsia, abdominal pain and vomiting. He has type 1 diabetes and missed several insulin doses. Vitals: HR 110 bpm, BP 100/60 mmHg, RR 28 breaths/min, Kussmaul respirations. Venous blood gas shows pH 7.12, bicarbonate 10 mmol/L, ketones strongly positive, glucose 24 mmol/L. What is the most appropriate initial fluid resuscitation?