My DD was really sleepy at the start, wouldn't feed, and lost a lot of weight, so I was advised to do top-ups too. It worked well for us, she gained weight well, and then with a lot of effort we were able to get to exclusively breast fed at 7 weeks.
What I was told to do was always to start with a breast feed (both breasts), and then afterwards offer a bottle - 80ml each time at the start iirc, but worth getting the advice of a health professional. That means you get the breast stimulation you need to make more milk, but your baby gets the milk she needs. They told me to express as well, but that never worked for me - it was exhausting to do all 3, which I found counter-productive. (Total respect to you for expressing for 5 months last time, by the way!!!)
I was very happy with mixed feeding, and intended to carry on indefinitely, but at about 2 weeks a HV told me that if I wanted to BF, then I needed to start cutting down the top-ups, since if I didn't get it sorted by 6 weeks, then I'd probably stop BF sooner than I'd like: apparently, up to 6 weeks your hormones mean you make lots of extra milk, but after that time it depends on demand, and tends to dwindle if you mix.
I was initially really upset at hearing such a negative take on what I thought was working.. and thought she was just being mean! In retrospect, I'm really glad she told me, because it meant I knew about the time limit, and really pushed to get the top-ups down. I started only offering top-ups after some feeds, and limiting the amount I offered. It took a lot of resolve, since DD did get upset when the milk ran out. And it meant I had to feed more often, which was tiring - but of course that's how you stimulate your supply. Within a couple of weeks I had it down to 90-120 ml of formula a day, but I really struggled to get rid of the top-ups completely. We almost had it cracked at 5 weeks, but then the 6-week growth spurt came along, and DD got really hungry, so it eventually took us until she was 7 weeks.
It sounds so easy reading back - but it wasn't. Struggling to feed your baby is traumatic and awful. But I now find breast-feeding an absolute joy, and I'm really, really grateful that we were able to get there. DD is now 7 months old, and I don't want to stop!
I had the help of a fantastic lactation consultant. I don't know where you are: if you're in SW London, pm me if you want her details. I'd really recommend getting some help. When the latch is right, it all works much better. I'm pretty sure we wouldn't have been successful without her help.
Oh, and DD did get nipple confusion, especially when she was tired - in both directions. Sometimes, she'd really struggle to latch onto the breast, and sometimes, she'd open her mouth really wide around the bottle teat instead of sucking it. It was a bit painful to watch (especially the bottle - since it was obvious that she was trying to suck a breast, and that it wouldn't work) but she always figured it out after a few minutes. I guess, given that she was doing both so regularly, she didn't really forget either completely.
All the best, and I hope it works well for you this time, however you decide to do it.