Basal insulin is a long acting insulin (usually 24 hours). A single injection counteracts the glucose produced by the liver throughout the day. Bolus insulin is the insulin taken before each meal and snack to counteract the carbs that you eat. You would have to use "carb counting" to determine the size of your bolus doses. I need 1 unit of bolus insulin for every 6 carbs I eat. Yours might be quite different. Maybe 1 unit for every 15 carbs, or 1 unit for every 30 carbs, etc. You could determine your number by trial and error. Starting with 15 and then increasing or decreasing as needed would give you your appropriate number. Some doctors prescribe that technique.
Your 75/25 is a mixture of basal and bolus insulins but it does not enable you to take the appropriate doses of bolus insulin for each meal. You are getting very rough approximations of the doses you would be taking if you used the basal and bolus insulins from seperate vials. Sometimes the 75/25 is giving you too little, or too much, bolus insulin. That causes highs and lows throughout the day. With basal/bolus you would have to take several shots each day. That may not sound appealing, but the much improved control with a more stable blood sugar level certainly makes it worthwhile. I hope you will talk to your doctor about using basal/bolus.
The basal insulins in the USA are usually Lantus ot Levemir. The bolus insulins are usually Humalog, Novolog or Apidra.
To learn about carb counting and other aspects of basal/bolus control you could make an appointment with a CDE (Certified Diabetes Educator). You can usually find a CDE in the diabetes education center of a hospital.