Newbie stability question

First time posting so go easy on me.
I bought an isup a couple of months ago and have been trying to use it. I find that it is really tippy and I can only paddle any distance if the water is flat. Any chop or wind and I'm off. I never feel at ease and it feels like I'm teetering on the edge the whole time. I'm 98 kilos and the board is a Honu Byron - 10'6" x 32", 4.75" thick and 245 litres. My wife is about 65 kilos and she seems much more planted and at ease on it.
I was wondering if a larger board might be more suitable for a beginner like me. Something like a Fanatic 13'6", 36" wide and 400 litres. I realise that experienced paddlers would probably regard this as a barge but I'm thinking it might be right for me at this stage. The way it's going now I'm losing interest and I'll probably give it away as I just don't think I'm getting anywhere. I'm just as hopeless now as when I first got on the board.
I'm interested in what people think about it, especially if anyone has been in the same situation.

Cheers

Is it pumped to recommended PSI? I didn't have a gage for a bit and wouldn't inflate enough, reduced stability a lot

My first SUP was an inflatable 10'2" x 30 x I cannot remember how many litres volume. I could stand on it in still water, but as soon as there was a hint of wind, chop, or water movement.. Down I go. I am heavier than you, but I also have close to two decades of surfing and skateboarding experience. I eventually managed to master staying on it and even surfing with it, but it took a lot of time (practising every day in progressively worse conditions).

Looking back at it now, I was wasting my time and didn't want admit that to myself, because I am stubborn. If I had got myself an appropriately sized board earlier, or better yet, an appropriately sized hard board earlier, then my progression would have been faster and easier.

I remember one windy and choppy day I got so frustrated that I hired a 12' something" x 34 Fanatic and it was super stable and easy in those conditions. I did that to prove to myself whether the board was the issue. Long story short, your board is too small for you, as the others have said. I don't think you need a 36" wide board, but look for something in the 12' long by 32 or 34 inches wide, if you really want to stick with an inflatable. If you plan to paddle more than once a month, then get a hard board.

As others have said, the problem is not with you, it is with inflatables. They are slow and very unstable compared to a hard board. I paddle at least 120 days a year in conditions ranging from an 8' board in double overhead surf to a 16' downwind race board in 35 mph open ocean winds. The most unstable I have ever felt is the few times I have paddled inflatables, even on a flat lake. If you want to enjoy paddling with stabiity and reasonable performance, I would go to a hard board. I think your idea of going to the huge Fanatic inflatable would be a mistake because it is still going to feel wobbly, will be horrilby slow. and it will get pushed around by the wind even more than your current board.
I think you have two good options to consider. If you are looking for a great allround board, someone mentioned the Sunova One and I think the 10'11" X 34" @ 203 liters would be a great choice. If you are hoping to develop faster paddling skills and you don't expect to be in surf, I would consider looking for a Touring style board at around 12'6" X 32" X 6' to 7" thick @ around 290 to 310 liters. Touring boards are far faster than allround boards and have incredible glide almost like race boards, just don't plan on taking them into the surf which you could do with the Sunova One.
Best of luck. If you can find the right hard board, you will start having fun.