19" would definitely be huge and there won't be any security at all. I just sold my 18" Stubben Siegfried because it was just too big and it has taken me months to convince myself of this because it was in SUCH beautiful condition. I tried to be in denial about the size. But I also ride a 16 1/2" dressage saddle which is PERFECT for me so I found the Stubben collecting dust and I finally decided what's the point in having it when I don't ride it. So I sold it just a couple of weeks ago and found a really good condition 17" Stubben Loreley. What a difference just the one inch makes. And hey, Delfina, no need to hide. There are others of us who ride "kiddi saddles".
And I'm no kid or even that petite. I celebrate my 39th next week but I'm a 5'11" rail. I have no butt. I slapped some 60" leathers on my 16 1/2" dressage Crosby and I feel so good in that saddle, I could jump fences in it. I think it's the deep dressage seat. I've actually opened up my thoroughbred on our make shift track in this saddle and let him fly and I wasn't going anywhere. I LOVE this saddle. Anyway to the OP, you definitely look like a 17-17 1/2" candidate. There are a ton of Stubbens on Ebay
and many of the older ones go for very reasonable prices, like under $300. You'll find one.