Toddler Behaviour/Tantrums

I'm really struggling with my toddler. He has always been a highly sensitive child, but recently the tantrums have been something else and I honestly feel like I'm losing the will! Everything is a meltdown, even the slightest things seem to set him off and all of a sudden he's throwing himself to the ground screaming. It doesn't help that we're in a major boundary testing phase so every time I need to step in and correct him it gets ten times worse. I try my best to be calm whilst still setting boundaries, to plan activities, to get him outside to burn off energy but the more effort I put in the worse he actually seems to get. It's exhausting! It sounds awful but I dread the days I'm alone with him because I'm so burnt out from the overstimulation. He tantrums, this upsets my other baby who then starts crying, he's then throwing himself all over me, kicking me, headbutting me, climbing on me, screaming in my ear, but when I try to comfort him he doesn't want it and pushes me away. I try to give him lots of 1 to 1 time, which he doesn't seem to want either. Even something as simple as going to the park (which he usually loves) is now a battle. It's to the point where I'm not really able to take him out anywhere as I can't manage with his meltdowns on my own, while also looking after a young baby. Thankfully we have a big garden so at least we can get out most days for a run around, but I'm relying on screen time more than I'd like just for a bit of quiet as some days my head feels like it's splitting with the constant noise. Is anyone else going through this? If so, how are you managing and do you have any tips? He is a bit behind on the communication and understanding front which makes things worse as it is obviously frustrating for him. I have spoken to the HV about this, but they told me they'd review it in his 2 year check. Everyone I seem to speak to in person seemingly has perfect toddlers, who don't behave this way so can't relate.