Ah yes I can sure relate. I lost my perfect horse, a beautiful mare named Maggie, in 2015, I got my boy Alex a few months after, he was a lot more forward going, bit spooky and cheeky but no vices. He did shake my confidence honestly, but the "leap" between them was achievable. Deep down, I still missed her and I think I struggled to trust him and bond with him even though I love and care for him immensely and we had a lot of fun. Then in 2019 he had to retire, I took 6 months to buy a second horse, tried to be really careful, eventually, bought an ID mare, Maisey, she's gorgeous and very well bred, but honestly I didn't notice any of that, she didn't look like Maggie but she put me in mind of her in the way she felt to ride and her attitude. I felt with a bit of tlc she'd be a similar diamond.
Well, once she'd had the tlc, i found she's not really anything like Maggie,( except for being pretty bombproof and sensible generally). She is a lot more forceful in her opinions and not all that patient and not the novice friendly ride I was very clear about requiring when i viewed her. Though I guess we did rub along ok for the 3 months or so that I rode her before it all unravelled and she bucked me off. Nappiness was a major factor, however, I do think pain, or at least discomfort, is a factor- she has had ulcers, hock and back problems and I suspect some kind of hormonal issue at various times. So, I don't ride her. I'd like to say I want to, but honestly I don't, I have lost my nerve....I might one day if the circumstances are right, but so far, it's not worked out like that. I've had well meaning friends try and push it but every time we reintroduce the saddle something happens, last year it was her back, this time it was ulcers again. I find I enjoy her best when there's no pressure or expectation, we long line and do groundwork and clicker training etc .
I guess this is a lot of words to say don't put pressure on yourself or the situation, it's not a race, take your time and do what works for you and your new horse. It may work out yet, or it may not, that is just how it is with horses. Losing a much loved horse is very hard, and no horse will ever replace them of course, but each will bring you sometime special and unique to the two of you.