Hi Mathildas mum!
Just wanted to also give you some encouragement, and tell you to keep going, I know it sounds cliche, but things do get better. My DS is now 5.5 months old, but we got him on EASY at 4 months and he was doing well until about 4.5 months when things starting going crazy. He would nap for 30-45 minutes at a time, and woke up every half hour or every hour at night, so I know how you feel. I get together with a mom's group that all have babies that are in the 4-5 month range, and most of them look like they want to pull their hair out and scream! We call it the 4 month sleep regression, don't know if there is actually such a thing, but it seems to be a trend anyway.
Anyway, just wanted to let you know that you're definately not alone. I also was not a big fan of PU/PD as I found it exhausting (my DS is over 20 pounds already and very heavy for me!) but I got some great advice from another mom on the BW website: try extending activity times by 15 minutes for 3-5 days and see if that helps you to extend the length of the naps. So for example if your lo wakes at 7:00am and usually goes down for a nap at 8:45am, try waiting another 10-15 minutes before putting her down to sleep, say 9:00-ish, and see if that helps. I know my little guy was a bit tired and fussy while we tried to extend his "A" time, so I would just walk around the house with him for the 10-15 minutes to calm him, and then put him to sleep, and it worked wonders for me.
Hope this helps, I'm definately not an expert at this, but thought I'd share our experience in hopes that it'll help you. (Another thing that helped us greatly was just to take a few days and let our lo sleep wherever and whenever he wanted, just to fill his "sleep banks" so that we were all a bit more rested before we started trying to get back on track again.)
Anyway, this is a long post, so I'll go now, but really hope this helps you!