Newbie to SUP - need advice re board type, length and width etc

Hello, Big Stewy here, in Essex, UK.

I tried SUP this morning in a local river with my son and loved it. I am really interested in buying a couple of boards - one for each of us. He has been a few times before with his girlfriend and I have another son and two daughters who will also try it out too. I dont want to spend a fortune at the moment, in case it is a fad!, maybe £300-400 per board. If I become hooked … well I might buy something better!!!

My issue is that I am 54 years old, 6’6" tall, weigh 116kg am fairly fit and have a high centre of gravity. My son is 23 years old about 6’4" and 98kg, fit and likes a challenge (!) and also has high COG. We could both stand up and paddle today, but I think I need a bigger board (more volume?). My poor old board sat a bit low in the water - well the deck was awash quite a bit and I was a bit wobbly on calm water. Partly that will be a complete lack of experience but I wonder if I need a wider/longer board? more volume, etc???.

Can anyone give me an idea about the length, type and width, thickness etc of a SUP that I should be looking at for me and for my son please?

I think we will be doing freshwater lakes and river boarding for the moment and not racing - only touring probably. I like the idea of sticking a rucksack on the front and paddling for a couple of hours upriver if that helps.

We used borrowed 10’ long x 33" wide boards today - cheap ones that worked fine.

Great to be here, any advice gratefully received,

thank you