The vivid dreams do suggest your sleep is getting more robust, and you should be assured the REM dream stage usually comes after the deeper, more refreshing NREM stages. All of which suggests you're getting some quality shut eye. As for waking up "mid-dream", it could be that the dream stage is actually ending, that's when sleep is lightest and we're more likely to awaken. Use that time to practice in bed relaxation methods to help yourself fall back asleep. Consider using a full CBT sleep training system for a comprehensive solution.