strawberries are fine on keto in small amounts as are blackberries and raspberries.
Keto is a funny thing you can't do half and half you have to go for it or not. The nature of ketosis means that you will feel dreadful if you keep starting and stopping. The first week IS quite hard but then it gets easier and you feel great. There is a low carb bootcamp on mumsnet which is excellent, usually there is one starting this time of year.
If you want to give it a go I suggest you strictly meal plan for two weeks include snacks and see how you feel at that point
Food ideas - breakfast, natural yogurt with strawberried and almonds, 2 eggs scrampled with butter, cheese, tomato and and ham ommlette.
Lunch, keto soup, bacon and veg, cream of chicken, mushroom, no bread. OR salad with protein, eggs, cheese or meat.
DInner - Sirfry veg with chicken cooked in garlic and soy sauce
Creamy chicken wrapped in bacon and garlic, cream and mushroom sauce.
Salmon cooked in butter and garlic with green beans
Sausages (black farmer are good for keto) with mediteranian veg pan fried with tomato and parmesan. etc etc.
Snacks, - boiled egg, 2 squares of dark choclate, a tablespoon of peabut butter, babybel, cucumber sticks.
If you want to start slower, just cut out the big four. bread, rice, pasta and potato. and anything sweet/processed.