I think it's really more about what you feel you need. It might be worth just having a few initial meetings with some of the doulas local to you. You might find someone you immediately hit it off with and know will be right for you. If not, then you will more than likely have plenty of support from your husband and midwife, particularly if it's one midwife you see at every appt who will be guaranteed to attend your birth, that it might not be worth hiring someone else who doesn't feel quite right. Personally, I'm a big believer that it's better to forgo a doula than to choose someone simply because you have limited options, even if they aren't right for you. There were only 2 doulas in my area and I interviewed both of them. One had too much nervous energy and seemed uncomfortable talking to me. The other one seemed nice enough, though some of her behaviour after we met (she basically fell off the radar for 3 weeks when I tried to book her) left me with a lot of qualms about hiring her. It was my first and I really wanted a doula so I booked her anyway as I didn't have any other options. She went on holiday for a month when she should have been on call for me, despite me telling her I felt I'd go on the earlier side and I was concerned she wouldn't be back in time. I went into labour the night before she got back and she had to race straight from the airport to make it. She missed most of the birth and did pretty much nothing except make me a cup of tea. Total waste of time and money and she was just in the way. Now that's not normal behaviour for most doulas (actually my best friend is a doula, but lives too far away to be mine), but what I'm trying to say is that my gut said she wasn't right. If you had someone before who you really bonded with and if you can't find anyone else you're comfortable with, I wouldn't risk bringing someone into the mix who isn't quite right. But you never know, you might find someone you really click with, so it's worth a try. Could you possibly ask your old doula if she could recommend anyone? Most doulas work with back-ups they trust or at least have doula friends in the area and she might know someone who would be perfect for you. Can't hurt!
But I very much agree with MarineWAG. If you are confident about your birth choices and are already surrounded by people who support you, you'll very likely be just fine. I didn't even really have a doula for my first birth (all natural home birth) and I felt like I was well supported. I don't plan to hire a doula next time.