Hi Moomin, welcome an congrats.
I go to quite a range of gym classes, and I've spoken to my gp, midwife and gym instructors about it. I felt it was important to say to gym instructors, partly because i worry that morning sickness could get the better of me mid class. I swore the instructors to secrecy/discretion, and definitely don't want to be singled out as pregnant until I'm ready for the news to be public.
I was doing a lot of high intensity stuff, so I have cut the most intense classes, but otherwise you don't really need any modification at this stage of pregnancy. Advice is to carry on doing what you normally do, just not doing anything so strenuous you're completely out of breath (Im finding I tire more easily anyway, so def cant give it 100%)
In terms of yoga, most styles should be fine, but you just need to be careful with (or not do) inversions, and hot yoga is a NoNo. I had a strong hot yoga practise before, so I'm really missing that. From my experience of hatha, you should be totally fine. Its only in tri 2 that you need to modify (e.g. not good to lay on your back for long periods). Exercise and meditation are so good for you and bub, so do keep it up!
I appreciate it's news you want to keep a lid on for now, but I recommend going early for a quiet word with your teacher - she'll be able to give you subtle advice and modifications to keep you safe.
Happy tri1
xx