Much much sympathy winging its way in your general direction!
Of course routines are important, but you prob already know much of this given this is your second DC (unless first one was incredibly laid back
)
Firstly, what time are his naps? Is there a big gap between am & pm ones?
Many babies benefit from the 2-3-4 (ish) pattern around this age. That is 2 naps, 1st approx 2 hrs after waking, 2nd approx 3hrs after waking and bed 4 hrs after final waking. Obv not to the letter, but basically the gap goes 'shorter', 'bigger' 'biggest'
Secondly, it is better to have the morning nap shorter than the pm nap, so if it looks like he's going to sleep longer than 1.5hrs in the am, I'd (shudder!) wake him. Try to resettle if he wakes after 50mins/1hr in pm nap.
Thirdly - being blw, does he get snacks between meals in addition to bf?
When I started weaning, DS was ebf & we did blw. I also offered snacks mid morning and mid afternoon (rice cakes, fruit, those organic pseudo-crisps etc) which helped him get the hang & fill him up a bit. Admittedly I started spoon loading and by about 8mo I was regularly spooning it in for him, though I still reckon that's baby-led as he actively encouraged it - though that's another thread
Once you are fairly confident he is getting enough food/bf in the day, set a time after which you won't feed. With my DS i would give last bf just before bed 7pm and then would not feed until a wake up after 11pm. Then I wouldn't feed until a wake up after 4am. Wake ups during this time were settled with dummy and patting. Or holding/rocking if escalating. DH helped. in fact he settled quicker with him, likely coz he couldn't smell milk/knew it wasn't going to happen with DH! As weaning progressed he become less enthusiastic about night feeds and now he just had 'booby breakfast' at 6-6.30ish
You see, around the 7mo stage my DS sounds like he was v similar to yours, had sleep all over the place and though not totally fixed, doing the things above has helped no end and now (nearly 10mo) we expect get 5-6, even 7hr stretches from him on a regular basis with relatively easy settles when he does have a wake (generally dummy & reposition as he's got himself tangled up in the corner of the cot)
Hope he gives you some decent stretches soon 