Not clear what you mean by bond rally, price or interest rate. Given the yield on the 30 year bond is barely above 1%, there's not much downside, which would indicate bond prices have nowhere to go but up. Price and yield move in opposite directions, if the yield goes up, the bond price goes down.
As an aside, Ray Dalio just said recently on Bloomberg that "you'd be pretty crazy to hold bonds".
In any case, if you think that TLT, or for the shorter terms something like SHY (1-3 years) and IEF (7-10 years) are not going to get you there, then you may need to consider leveraged products like options and futures.
Depending on the amount of money you have, regular futures may not be an option given the notional value is very large ($100,000 per contract for 5+ years, with initial margin that will vary depending on your broker and the product). For bonds, I'm not aware there are mini or micro contracts which would be suitable for smaller accounts.
Options might an other thing you could consider for a smaller account, although you need to be right on both the direction, and the timing, as options will decay (if you buy them), and expire. Simplest strategy could be to buy calls on one of the ETF above.
Either way, based on how you framed your question, you'll need to do a lot of research on your own rather that rely on advice you could find here, using leverage is one of the surest way to go bust quickly.
Note: this is not financial advice, and is just for educational purposes (if such a warning is required here).
Edit: to amend the Ray Dalio's quote to make it more accurate.
