Two bits of caution...
The first is that the SRD is limited but not done so from the perspective of making things "simpler". The intent of the SRD is to provide a publishing resource for people. You might already be aware of that, but it seems like people these days think of the SRD as "basically complete but simplified". It's reduced options in many but not all cases, but it's primarily intended to be a licensed set of rules that people can use for a variety of purposes.
Second, I would urge caution when you're starting to talk about "balanced", equivalent options, etc. "Balance" get bandied about as if it's some sort of objectively neutral measurement, where you can draw a line and declare [x] to be balanced or [y] to be unbalanced.
The problem is, it's subjective. Anytime you have CR brought up for example, you've got tons of people going out of their way to talk about how subjective it is, how they can make "balanced" whatever that are completely broken... the same thing applies to classes and their abilities.
Sure, some things can be more clearly seen to be unbalanced in relation to others. But the degree of imbalance will vary depending on the player(s) and how skilled/interested they are in optimising, the situation the classes/class abilities are going to be featured within, the adventure/opposition, etc.
Or, to reframe it slightly...
You're just as likely to achieve "balance" in this situation by turning 5e into a point-buy type system, like BESM. In fact, I'd personally argue that you're better off taking a specific approach like assigning points to features, as it'll mean at a rough glance, you can say that [x] is roughly equivalent to [y]. The actual value of the points? shrug It doesn't actually matter. You just have to decide a baseline for a set of points and then base the costs of everything else around that. You're not trying to get an exact match, point for point, with everything; you just need to be able to effectively say "in the typical situation, [this] is typically worth less/more than [that]". Yes, there will always be exceptions/edge cases. You shouldn't try to figure out every possible exception, instead you should design to the most common situations and then do what every GM does... make a call when an exception pops up.
You should consider looking at Anime 5e. I haven't for a number of personal reasons, but if you're really interested in going down a "balanced" path, this is probably going to be your best option, with a significant amount of heavy lifting done for you. The goal isn't to switch over to using the rules necessarily, but to use it as a framework to balance your game in a consistent fashion. And if there are imbalances, it'll be easier to pick up where that imbalance is and shift the point-cost if necessary, in a consistent fashion.
It'll also mean that when you've got point-costs for things, if you find something that needs to be changed, you can look at the other options that may not appear related but cost the same amount, and make adjustments there at the same time. That way, any fixes that you apply, you can migrate (with some work) consistently across the system.
