I would NOT recommend doing a Masters course to try and prolong the student experience. Postgraduate study is very different from undergraduate study. There is much more work, much higher intensity and the whole undergraduate social feel is gone, your fellow students are likely to be mostly international students who are all about work. Also the workload on a Masters means that it is harder to hold down a part time job and get all your work done as well, and there is no student loan coming in, so financially it is much harder as well.
I can understand the feeling regarding leaving uni...I had an amazing time when I was at uni and I remember it hit me when I left, I felt a bit lost and worried about the future. I do miss things about uni, I miss going to seminars and the challenge of writing essays, getting immersed in the research for them and then the excitement of getting them back and seeing what mark I got. I miss the less structured day and having more free time, and I miss living in a house with my student housemates and just spending time together doing nothing. I liked the feel of walking through campus in Leeds and still when I go back to Leeds if I have to walk through the city centre I always try and cut through the uni campus as it feels good to be there. I would still regard uni days as the best days of my life.
However....there is life beyond uni and there are some advantages, to really take advantage of them you have to get a job you want and are interested in though. When you start earning more money you can improve your living environment from cheap houseshares, afford better quality clothes, just live a more classy lifestyle. I found it easier to meet likeminded people in relationship terms, after leaving uni, and relationships are easier without being in the goldfish bowl of everyone around you knowing what's going on. You get used to working and you appreciate your time off more, now I look back at uni although I thought I was a motivated student, I did have a lot of free time and I wasted a lot of it lounging around doing nothing.