The kitchen one should be a rate of rise of temperature detector (if you burn the toast if won't trip it).
This is not my area of expertise but I would image that the only other place that needs a smoke detector is the hallway. I assume that you exit the flat via the hallway, if, bizarrely, you exit via bedroom, then, my understanding is that the bedroom would need a fire alarm.
I would advise that you buy interlinked sensors. In the event that a fire starts in the kitchen, and the kitchen door is closed, the hallway sensor will go off, meaning that if your bedroom door is closed, you will still hear the alarm.
Google- Fire Angel sensors. You can buy them at the likes of screwfix.
For safety you don't want to do the bare minimum as required currently in England & Wales. Hallway only (no need for kitchen as there is a door on it).
In NI/Scotland you would need interlinked Heat detector in Kitchen, Smoke in Hallway and another Smoke in Lounge. 3 alarm 10 year battery kits cost around the £80 mark.
The hallway one may need careful placement away from any steam from kitchen and/or bathroom to ensure no false alarms.
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