New lurcher puppy bites hard – help

Hi! My partner and I rehomed a lurcher puppy a week ago. He's 13 weeks now, he had to be taken away alongside his litter for welfare reasons, they were malnourished, full of fleas and worms, that's all we know. He was taken away roughly when he was 6 weeks. He was with the Scottish SPCA alongside his litter mates until we adopted him. He is also the "runt of the litter", he's half the size of his siblings now. A throwaway comment from the rescue was that despite his size he was the one to "bully" his siblings, I assume as a coping skill for being so smol.

I had an adult rescue lurcher before but this is a whole other thing.

He really struggles to settle and sleep during the day and as a result he gets more and more nightmareish as the afternoon and evening goes on.

He sleeps in his crate in our bedroom overnight, door open, usually after he falls asleep on one of us and then we put him there.

However, when he's overstimulated he bites HARD. I mean he latches onto your skin and flesh and will NOT let go.

The usual advice of freeze, stop giving attention, redirect works with his biting when he's not overtired but does absolutely nothing when he gets in this state, if anything he just bites harder.

I work from home full time so we want make more of an ironclad routine for naps during the day to improve his sleep and hope behavior will follow. In the meantime though I was hoping someone here could give us some advice – we welcome suggestions for calming him for napping (once he's too tired giving him kongs and chews does nothing, he just continues when he's done with them).

We have tried closing him in his crate a few nights ago, this being after he slept through the night in it a few times. We were met with increasingly panicked howls for just shy of 10 minutes before we gave in. Maybe we made a mistake trying but we didn't know how to calm him, or maybe we should have persevered?

But also, how do we keep our sanity and safety when he gets so hardcore with his bites? It is genuinely extremely painful and happens pretty much every night. 🥲 He is also growing quite rapidly and we worried these chomps going to become dangerous.

Help!