Daytime naos

[Zombiemum1]

I'm after some advice on how to make my almost 4 month old boy take longer naps in the day. He puts himself off to sleep beautifully in the day and sleeps for around 4-5 hours at night but only naps for 20-40 mins in the day and is subsequently very narky all day because of this. We use 'white noise' and a darkened room already and as I said, going off to sleep isn't a problem but staying asleep is...... anyone have any techniques/tips I could try please

Blackout dark room (can get a gro anywhere blind or cheaper alternative from amazon)
Sleeping bag and / or swaddle as you would for a night.
Although this may be normal for his age - at four months sleeping patterns change so they wake up after one sleep cycle (have a look at the 4 month sleep regression). This may be a phase that passes.
Also, it’s worth keeping an eye on the awake time as it’s really easy for them to become overtired and unable to link sleep cycles effectively - awake time shouldn’t be any longer than 2-2.25hrs - it should be as close to that as possible, any less and he may not be tired enough to sleep longer.
I’d expect 3 naps per day totalling 3-3.5hrs between a roughly 7-7 day.

My five month old dd sleeps best in the day when I feed her to sleep and then lay or sit next to her. I usually look on my phone or read and she occasionally wakes up, checks I'm still there and goes straight back to sleep. She can sleep for a few hours like this. She has much shorter naps if she's in the pram or if I try and get anything else done!